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Jamb Mathematics - Lesson Notes on progression for UTME Candidate

Feb 09 2025 07:51 PM

Osason

Jamb Updates

Progression | Jamb Mathematics

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Cadet, listen up! Your next mission is to master the art of progression—arithmetic, geometric, and beyond—because precision and strategy are key to victory. Drill through formulas, decode patterns, and sharpen your problem-solving skills, because only the well-prepared survive the battlefield of mathematics. Fall in and get to work! 🚀🔥
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Are you preparing for your JAMB Mathematics exam and feeling a bit uncertain about how to approach the topic of Progression? Don’t worry—you’re in the right place! This lesson is here to break it down in a simple, clear, and engaging way, helping you build the strong foundation you need to succeed. Whether you're struggling with complex questions or just seeking a quick refresher, this guide will boost your understanding and confidence. Let’s tackle Progression together and move one step closer to achieving your exam success! Blissful learning.
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Calculation problem involving arithmetic progression

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1. Find the 10th term of the AP: 2, 5, 8, 11, ...
Solution: The formula for the nth term of an AP is: an=a+(n1)da_n = a + (n-1) d Where:
  • a=2a = 2 (first term),
  • d=52=3d = 5 - 2 = 3 (common difference),
  • n=10n = 10.
a10=2+(101)3a_{10} = 2 + (10 - 1) \cdot 3
=2+93= 2 + 9 \cdot 3
=2+27=29= 2 + 27 = 29
Answer: 2929

2. Find the sum of the first 15 terms of the AP: 3, 7, 11, 15, ...
Solution: Sum of the first nn terms of an AP is given by: Sn=n2(2a+(n1)d)S_n = \frac{n}{2} (2a + (n-1)d)
Here,
  • a=3a = 3,
  • d=73=4d = 7 - 3 = 4,
  • n=15n = 15.
S15=152(23+(151)4)S_{15} = \frac{15}{2} (2 \cdot 3 + (15 - 1) \cdot 4)
=152(6+56)= \frac{15}{2} (6 + 56)
=15262= \frac{15}{2} \cdot 62
=1531= 15 \cdot 31
=465= 465
Answer: 465465

3. The 7th term of an AP is 20, and the 13th term is 50. Find the first term and common difference.
Solution: Using the formula: an=a+(n1)da_n = a + (n-1)d
For a7=20a_7 = 20: a+6d=20a + 6d = 20
For a13=50a_{13} = 50: a+12d=50a + 12d = 50
Subtracting equations: (a+12d)(a+6d)=5020(a + 12d) - (a + 6d) = 50 - 20
6d=306d = 30
d=5d = 5
Substituting dd in a+6(5)=20a + 6(5) = 20: a+30=20a + 30 = 20
a=10a = -10
Answer: a=10a = -10, d=5d = 5

4. Find the number of terms in the AP: 4, 10, 16, ..., 88.
Solution: Using an=a+(n1)da_n = a + (n-1)d,
  • a=4a = 4,
  • d=104=6d = 10 - 4 = 6,
  • an=88a_n = 88.
88=4+(n1)688 = 4 + (n-1)6
884=(n1)688 - 4 = (n-1)6
84=(n1)684 = (n-1)6
n1=14n - 1 = 14
n=15n = 15
Answer: 1515

5. The sum of the first 20 terms of an AP is 1000. The first term is 7. Find the common difference.
Solution: Using Sn=n2(2a+(n1)d)S_n = \frac{n}{2} (2a + (n-1)d),
1000=202(27+(201)d)1000 = \frac{20}{2} (2 \cdot 7 + (20-1)d)
1000=10(14+19d)1000 = 10 (14 + 19d)
100=14+19d100 = 14 + 19d
86=19d86 = 19d
d=8619=4.526d = \frac{86}{19} = 4.526
Answer: d=4.526d = 4.526

6. Find the 12th term of the AP: 6, 13, 20, 27, ...
Solution: Using an=a+(n1)da_n = a + (n-1)d,
  • a=6a = 6,
  • d=136=7d = 13 - 6 = 7,
  • n=12n = 12.
a12=6+(121)7a_{12} = 6 + (12-1) \cdot 7
=6+117= 6 + 11 \cdot 7
=6+77=83= 6 + 77 = 83
Answer: 8383

7. Find the sum of the first 25 terms of the AP: 2, 8, 14, 20, ...
Solution: Using Sn=n2(2a+(n1)d)S_n = \frac{n}{2} (2a + (n-1)d),
  • a=2a = 2,
  • d=82=6d = 8 - 2 = 6,
  • n=25n = 25.
S25=252(22+(251)6)S_{25} = \frac{25}{2} (2 \cdot 2 + (25-1) \cdot 6)
=252(4+144)= \frac{25}{2} (4 + 144)
=252148= \frac{25}{2} \cdot 148
=2574= 25 \cdot 74
=1850= 1850
Answer: 18501850

8. Find the number of terms in the AP: 3, 7, 11, ..., 87.
Solution: Using an=a+(n1)da_n = a + (n-1)d,
  • a=3a = 3,
  • d=73=4d = 7 - 3 = 4,
  • an=87a_n = 87.
87=3+(n1)487 = 3 + (n-1)4
873=(n1)487 - 3 = (n-1)4
84=(n1)484 = (n-1)4
n1=21n - 1 = 21
n=22n = 22
Answer: 2222

9. The 8th term of an AP is 36, and the 16th term is 84. Find the first term and common difference.
Solution: Using an=a+(n1)da_n = a + (n-1)d,
For a8=36a_8 = 36: a+7d=36a + 7d = 36
For a16=84a_{16} = 84: a+15d=84a + 15d = 84
Subtracting equations: (a+15d)(a+7d)=8436(a + 15d) - (a + 7d) = 84 - 36
8d=488d = 48
d=6d = 6
Substituting dd in a+7(6)=36a + 7(6) = 36: a+42=36a + 42 = 36
a=6a = -6
Answer: a=6a = -6, d=6d = 6

10. The sum of the first 30 terms of an AP is 2400. The first term is 10. Find the common difference.
Solution: Using Sn=n2(2a+(n1)d)S_n = \frac{n}{2} (2a + (n-1)d),
2400=302(210+(301)d)2400 = \frac{30}{2} (2 \cdot 10 + (30-1)d)
2400=15(20+29d)2400 = 15 (20 + 29d)
160=20+29d160 = 20 + 29d
140=29d140 = 29d
d=14029=4.83d = \frac{140}{29} = 4.83
Answer: d=4.83d = 4.83

11. Find the 20th term of the AP: 50, 45, 40, 35, ...
Solution: Using an=a+(n1)da_n = a + (n-1)d,
  • a=50a = 50,
  • d=4550=5d = 45 - 50 = -5,
  • n=20n = 20.
a20=50+(201)(5)a_{20} = 50 + (20-1)(-5)
=5095= 50 - 95
=45= -45
Answer: 45-45

12. Find the sum of the first 12 terms of the AP: 5, 10, 15, ...
Solution: Using Sn=n2(2a+(n1)d)S_n = \frac{n}{2} (2a + (n-1)d),
  • a=5a = 5,
  • d=5d = 5,
  • n=12n = 12.
S12=122(25+(121)5)S_{12} = \frac{12}{2} (2 \cdot 5 + (12-1)5)
=6(10+55)= 6 (10 + 55)
=665= 6 \cdot 65
=390= 390
Answer: 390390

Here are the remaining 13 unique arithmetic progression (AP) problems with step-by-step solutions.

13. The 5th term of an AP is 25, and the 10th term is 50. Find the first term and common difference.
Solution: Using an=a+(n1)da_n = a + (n-1)d,
For a5=25a_5 = 25: a+4d=25a + 4d = 25
For a10=50a_{10} = 50: a+9d=50a + 9d = 50
Subtracting equations: (a+9d)(a+4d)=5025(a + 9d) - (a + 4d) = 50 - 25
5d=255d = 25
d=5d = 5
Substituting dd in a+4(5)=25a + 4(5) = 25: a+20=25a + 20 = 25
a=5a = 5
Answer: a=5a = 5, d=5d = 5

14. Find the number of terms in the AP: 7, 14, 21, ..., 133.
Solution: Using an=a+(n1)da_n = a + (n-1)d,
  • a=7a = 7,
  • d=147=7d = 14 - 7 = 7,
  • an=133a_n = 133.
133=7+(n1)7133 = 7 + (n-1)7
1337=(n1)7133 - 7 = (n-1)7
126=(n1)7126 = (n-1)7
n1=18n - 1 = 18
n=19n = 19
Answer: 1919

15. The sum of the first 40 terms of an AP is 8200. The first term is 15. Find the common difference.
Solution: Using Sn=n2(2a+(n1)d)S_n = \frac{n}{2} (2a + (n-1)d),
8200=402(215+(401)d)8200 = \frac{40}{2} (2 \cdot 15 + (40-1)d)
8200=20(30+39d)8200 = 20 (30 + 39d)
410=30+39d410 = 30 + 39d
380=39d380 = 39d
d=38039=9.74d = \frac{380}{39} = 9.74
Answer: d=9.74d = 9.74

16. Find the 25th term of the AP: 1, 4, 7, 10, ...
Solution: Using an=a+(n1)da_n = a + (n-1)d,
  • a=1a = 1,
  • d=3d = 3,
  • n=25n = 25.
a25=1+(251)3a_{25} = 1 + (25-1)3
=1+72= 1 + 72
=73= 73
Answer: 7373

17. Find the sum of the first 18 terms of the AP: 10, 20, 30, ...
Solution: Using Sn=n2(2a+(n1)d)S_n = \frac{n}{2} (2a + (n-1)d),
  • a=10a = 10,
  • d=10d = 10,
  • n=18n = 18.
S18=182(210+(181)10)S_{18} = \frac{18}{2} (2 \cdot 10 + (18-1)10)
=9(20+170)= 9 (20 + 170)
=9190= 9 \cdot 190
=1710= 1710
Answer: 17101710

18. The first term of an AP is -3, and the 21st term is 57. Find the common difference.
Solution: Using an=a+(n1)da_n = a + (n-1)d,
57=3+(211)d57 = -3 + (21-1)d
57+3=20d57 + 3 = 20d
60=20d60 = 20d
d=6020=3d = \frac{60}{20} = 3
Answer: d=3d = 3

19. The sum of the first 50 terms of an AP is 5050. Find the first term if the common difference is 2.
Solution: Using Sn=n2(2a+(n1)d)S_n = \frac{n}{2} (2a + (n-1)d),
5050=502(2a+(501)2)5050 = \frac{50}{2} (2a + (50-1)2)
5050=25(2a+98)5050 = 25 (2a + 98)
202=2a+98202 = 2a + 98
2a=1042a = 104
a=52a = 52
Answer: a=52a = 52

20. Find the 15th term of the AP: 100, 97, 94, ...
Solution: Using an=a+(n1)da_n = a + (n-1)d,
  • a=100a = 100,
  • d=97100=3d = 97 - 100 = -3,
  • n=15n = 15.
a15=100+(151)(3)a_{15} = 100 + (15-1)(-3)
=10042= 100 - 42
=58= 58
Answer: 5858

21. Find the number of terms in the AP: 50, 45, 40, ..., 5.
Solution: Using an=a+(n1)da_n = a + (n-1)d,
  • a=50a = 50,
  • d=5d = -5,
  • an=5a_n = 5.
5=50+(n1)(5)5 = 50 + (n-1)(-5)
550=(n1)(5)5 - 50 = (n-1)(-5)
45=(n1)(5)-45 = (n-1)(-5)
n1=9n-1 = 9
n=10n = 10
Answer: 1010

22. The 6th term of an AP is 19, and the 11th term is 34. Find the first term and common difference.
Solution: Using an=a+(n1)da_n = a + (n-1)d,
For a6=19a_6 = 19: a+5d=19a + 5d = 19
For a11=34a_{11} = 34: a+10d=34a + 10d = 34
Subtracting equations: (a+10d)(a+5d)=3419(a + 10d) - (a + 5d) = 34 - 19
5d=155d = 15
d=3d = 3
Substituting dd in a+5(3)=19a + 5(3) = 19: a+15=19a + 15 = 19
a=4a = 4
Answer: a=4a = 4, d=3d = 3

23. Find the sum of the first 22 terms of the AP: 8, 14, 20, ...
Solution: Using Sn=n2(2a+(n1)d)S_n = \frac{n}{2} (2a + (n-1)d),
  • a=8a = 8,
  • d=6d = 6,
  • n=22n = 22.
S22=222(28+(221)6)S_{22} = \frac{22}{2} (2 \cdot 8 + (22-1)6)
=11(16+126)= 11 (16 + 126)
=11142= 11 \cdot 142
=1562= 1562
Answer: 15621562

24. The sum of the first 60 terms of an AP is 18300. Find the first term if the common difference is 5.
Solution: Using Sn=n2(2a+(n1)d)S_n = \frac{n}{2} (2a + (n-1)d),
18300=602(2a+(601)5)18300 = \frac{60}{2} (2a + (60-1)5)
18300=30(2a+295)18300 = 30 (2a + 295)
610=2a+295610 = 2a + 295
2a=3152a = 315
a=157.5a = 157.5
Answer: a=157.5a = 157.5

25. Find the 30th term of the AP: -5, -2, 1, ...
Solution: Using an=a+(n1)da_n = a + (n-1)d,
  • a=5a = -5,
  • d=3d = 3,
  • n=30n = 30.
a30=5+(301)3a_{30} = -5 + (30-1)3
=5+87= -5 + 87
=82= 82
Answer: 8282

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Calculation problems involving geometric progression

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1. Find the 10th term of the GP: 3, 6, 12, 24, ...
Solution: The formula for the nth term of a GP is: an=ar(n1)a_n = a r^{(n-1)} Where:
  • a=3a = 3 (first term),
  • r=63=2r = \frac{6}{3} = 2 (common ratio),
  • n=10n = 10.
a10=3×2(101)a_{10} = 3 \times 2^{(10-1)}
=3×29= 3 \times 2^9
=3×512= 3 \times 512
=1536= 1536
Answer: 15361536

2. Find the sum of the first 6 terms of the GP: 5, 10, 20, 40, ...
Solution: The sum of the first nn terms of a GP is given by: Sn=a(rn1)r1,for r1S_n = \frac{a (r^n - 1)}{r - 1}, \quad \text{for } r \neq 1
Here,
  • a=5a = 5,
  • r=2r = 2,
  • n=6n = 6.
S6=5(261)21S_6 = \frac{5(2^6 - 1)}{2 - 1}
=5(641)= 5(64 - 1)
=5×63= 5 \times 63
=315= 315
Answer: 315315

3. The 4th term of a GP is 48, and the 7th term is 384. Find the first term and common ratio.
Solution: Using an=ar(n1)a_n = a r^{(n-1)},
For a4=48a_4 = 48: ar3=48a r^3 = 48
For a7=384a_7 = 384: ar6=384a r^6 = 384
Dividing both equations: ar6ar3=38448\frac{a r^6}{a r^3} = \frac{384}{48}
r3=8r^3 = 8
r=2r = 2
Substituting in ar3=48a r^3 = 48: a(23)=48a(2^3) = 48
a(8)=48a(8) = 48
a=6a = 6
Answer: a=6a = 6, r=2r = 2

4. Find the sum to infinity of the GP: 20, 10, 5, 2.5, ...
Solution: The sum to infinity of a GP is: S=a1r,for r<1S_{\infty} = \frac{a}{1 - r}, \quad \text{for } |r| < 1
Here,
  • a=20a = 20,
  • r=1020=0.5r = \frac{10}{20} = 0.5.
S=2010.5S_{\infty} = \frac{20}{1 - 0.5}
=200.5= \frac{20}{0.5}
=40= 40
Answer: 4040

5. Find the number of terms in the GP: 4, 12, 36, ..., 2916.
Solution: Using an=ar(n1)a_n = a r^{(n-1)},
  • a=4a = 4,
  • r=124=3r = \frac{12}{4} = 3,
  • an=2916a_n = 2916.
2916=4×3(n1)2916 = 4 \times 3^{(n-1)}
Dividing by 4: 29164=3(n1)\frac{2916}{4} = 3^{(n-1)}
729=3(n1)729 = 3^{(n-1)}
Since 729=36729 = 3^6,
n1=6n - 1 = 6
n=7n = 7
Answer: 77

6. Find the 8th term of the GP: 2, 6, 18, 54, ...
Solution: Using the formula: an=ar(n1)a_n = a r^{(n-1)} Where:
  • a=2a = 2,
  • r=62=3r = \frac{6}{2} = 3,
  • n=8n = 8.
a8=2×3(81)a_8 = 2 \times 3^{(8-1)}
=2×37= 2 \times 3^7
=2×2187= 2 \times 2187
=4374= 4374
Answer: 43744374

7. Find the sum of the first 5 terms of the GP: 1, 4, 16, 64, ...
Solution: Sn=a(rn1)r1S_n = \frac{a (r^n - 1)}{r - 1}
  • a=1a = 1,
  • r=4r = 4,
  • n=5n = 5.
S5=1(451)41S_5 = \frac{1(4^5 - 1)}{4 - 1}
=102413= \frac{1024 - 1}{3}
=10233=341= \frac{1023}{3} = 341
Answer: 341341

8. The 6th term of a GP is 81, and the 10th term is 6561. Find the common ratio.
Solution: a6=ar5=81a_6 = a r^5 = 81
a10=ar9=6561a_{10} = a r^9 = 6561
Dividing both: ar9ar5=656181\frac{a r^9}{a r^5} = \frac{6561}{81}
r4=81r^4 = 81
r=3r = 3
Answer: r=3r = 3

9. Find the sum to infinity of the GP: 8, 4, 2, 1, ...
Solution: S=a1rS_{\infty} = \frac{a}{1 - r}
  • a=8a = 8,
  • r=48=0.5r = \frac{4}{8} = 0.5.
S=810.5S_{\infty} = \frac{8}{1 - 0.5}
=80.5=16= \frac{8}{0.5} = 16
Answer: 1616

10. Find the number of terms in the GP: 3, 9, 27, ..., 2187.
Solution: 2187=3×3(n1)2187 = 3 \times 3^{(n-1)}
21873=3(n1)\frac{2187}{3} = 3^{(n-1)}
729=3(n1)729 = 3^{(n-1)}
n1=6n-1 = 6
n=7n = 7
Answer: 77

11. The sum of the first 7 terms of a GP is 5461. The first term is 1, and the common ratio is 2. Find S7S_7.
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Solution: S7=1(271)21S_7 = \frac{1(2^7 - 1)}{2 - 1}
=271= 2^7 - 1
=1281= 128 - 1
=127= 127
Answer: 127127

12. Find the 15th term of the GP: 5, 10, 20, ...
Solution: a15=5×2(151)a_{15} = 5 \times 2^{(15-1)}
=5×214= 5 \times 2^{14}
=5×16384= 5 \times 16384
=81920= 81920
Answer: 8192081920

13. The 9th term of a GP is 512, and the 3rd term is 8. Find the common ratio.
Solution: ar8ar2=5128\frac{a r^8}{a r^2} = \frac{512}{8}
r6=64r^6 = 64
r=2r = 2
Answer: r=2r = 2

14. Find the sum to infinity of the GP: 6, 2, 23\frac{2}{3},...
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Solution: S=a1rS_{\infty} = \frac{a}{1 - r}
  • a=6a = 6,
  • r=26=13r = \frac{2}{6} = \frac{1}{3}.
S=6113S_{\infty} = \frac{6}{1 - \frac{1}{3}}
=623= \frac{6}{\frac{2}{3}}
=6×32= 6 \times \frac{3}{2}
=9= 9
Answer: 99

15. The sum of the first 8 terms of a GP is 765. The first term is 3, and the common ratio is 2. Find S8S_8.
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Solution: S8=3(281)21S_8 = \frac{3(2^8 - 1)}{2 - 1}
=3(2561)= 3(256 - 1)
=3×255= 3 \times 255
=765= 765
Answer: 765765

16. Find the number of terms in the GP: 7, 14, 28, ..., 1792.
Solution: 1792=7×2(n1)1792 = 7 \times 2^{(n-1)}
17927=2(n1)\frac{1792}{7} = 2^{(n-1)}
256=2(n1)256 = 2^{(n-1)}
n1=8n - 1 = 8
n=9n = 9
Answer: 99

17. Find the sum to infinity of the GP: 12, 4, 43\frac{4}{3},..
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Solution: S=a1rS_{\infty} = \frac{a}{1 - r}
  • a=12a = 12,
  • r=412=13r = \frac{4}{12} = \frac{1}{3}.
S=12113S_{\infty} = \frac{12}{1 - \frac{1}{3}}
=1223= \frac{12}{\frac{2}{3}}
=12×32= 12 \times \frac{3}{2}
=18= 18
Answer: 1818

18. The sum of the first 10 terms of a GP is 3072. The first term is 1, and the common ratio is 2. Find S10S_{10}.
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Solution: S10=1(2101)21S_{10} = \frac{1(2^{10} - 1)}{2 - 1}
=2101= 2^{10} - 1
=10241= 1024 - 1
=1023= 1023
Answer: 10231023

19. Find the 20th term of the GP: 10, 5, 2.5, ...
Solution: a20=10×0.5(201)a_{20} = 10 \times 0.5^{(20-1)}
=10×0.519= 10 \times 0.5^{19}
=10×1524288= 10 \times \frac{1}{524288}
=10524288= \frac{10}{524288}
Answer: 10524288\frac{10}{524288}

20. Find the sum of the first 12 terms of the GP: 1, -1, 1, -1, ...
Solution: Since r=1r = -1, the sum alternates.
S12=1((1)121)11S_{12} = \frac{1( (-1)^{12} - 1 )}{-1 - 1}
=(11)2= \frac{(1 - 1)}{-2}
=0= 0
Answer: 00
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Calculation problem involving sum of the nth term of a geometric progression

paragraph
1. Find the sum of the first 7 terms of the GP: 2, 6, 18, 54, ...
Solution: The sum of the first nn terms of a GP is given by: Sn=a(rn1)r1,for r1S_n = \frac{a (r^n - 1)}{r - 1}, \quad \text{for } r \neq 1
Here:
  • a=2a = 2,
  • r=62=3r = \frac{6}{2} = 3,
  • n=7n = 7.
S7=2(371)31S_7 = \frac{2(3^7 - 1)}{3 - 1}
=2(21871)2= \frac{2(2187 - 1)}{2}
=2(1093)= 2(1093)
=2186= 2186
Answer: 21862186

2. Find the sum of the first 6 terms of the GP: 4, -12, 36, -108, ...
Solution: Using: Sn=a(rn1)r1S_n = \frac{a (r^n - 1)}{r - 1}
Here:
  • a=4a = 4,
  • r=3r = -3,
  • n=6n = 6.
S6=4((3)61)31S_6 = \frac{4((-3)^6 - 1)}{-3 - 1}
=4(7291)4= \frac{4(729 - 1)}{-4}
=4(728)4= \frac{4(728)}{-4}
=728= -728
Answer: 728-728

3. The sum of the first 8 terms of a GP is 3280. The first term is 5, and the common ratio is 2. Find S8S_8.
paragraph
Solution: Using: Sn=a(rn1)r1S_n = \frac{a (r^n - 1)}{r - 1}
  • a=5a = 5,
  • r=2r = 2,
  • n=8n = 8.
S8=5(281)21S_8 = \frac{5(2^8 - 1)}{2 - 1}
=5(2561)= 5(256 - 1)
=5(255)= 5(255)
=1275= 1275
Answer: 12751275

4. Find the sum of the first 10 terms of the GP: 1, 3, 9, ...
Solution: Using: Sn=a(rn1)r1S_n = \frac{a (r^n - 1)}{r - 1}
  • a=1a = 1,
  • r=3r = 3,
  • n=10n = 10.
S10=1(3101)31S_{10} = \frac{1(3^{10} - 1)}{3 - 1}
=31012= \frac{3^{10} - 1}{2}
=5904912= \frac{59049 - 1}{2}
=590482= \frac{59048}{2}
=29524= 29524
Answer: 2952429524

5. Find the sum of the first 9 terms of the GP: 7, 21, 63, ...
Solution: Using: Sn=a(rn1)r1S_n = \frac{a (r^n - 1)}{r - 1}
  • a=7a = 7,
  • r=3r = 3,
  • n=9n = 9.
S9=7(391)31S_9 = \frac{7(3^9 - 1)}{3 - 1}
=7(196831)2= \frac{7(19683 - 1)}{2}
=7(19682)2= \frac{7(19682)}{2}
=68887= 68887
Answer: 6888768887

6. The sum of the first 5 terms of a GP is 242. The first term is 2, and the common ratio is 3. Find S5S_5.
paragraph
Solution: Using: Sn=a(rn1)r1S_n = \frac{a (r^n - 1)}{r - 1}
  • a=2a = 2,
  • r=3r = 3,
  • n=5n = 5.
S5=2(351)31S_5 = \frac{2(3^5 - 1)}{3 - 1}
=2(2431)2= \frac{2(243 - 1)}{2}
=2(121)= 2(121)
=242= 242
Answer: 242242

7. Find the sum of the first 7 terms of the GP: 5, 10, 20, 40, ...
Solution: Using: Sn=a(rn1)r1S_n = \frac{a (r^n - 1)}{r - 1}
  • a=5a = 5,
  • r=2r = 2,
  • n=7n = 7.
S7=5(271)21S_7 = \frac{5(2^7 - 1)}{2 - 1}
=5(1281)= 5(128 - 1)
=5(127)= 5(127)
=635= 635
Answer: 635635

8. Find the sum of the first 12 terms of the GP: 3, 6, 12, ...
Solution: Using: Sn=a(rn1)r1S_n = \frac{a (r^n - 1)}{r - 1}
  • a=3a = 3,
  • r=2r = 2,
  • n=12n = 12.
S12=3(2121)21S_{12} = \frac{3(2^{12} - 1)}{2 - 1}
=3(40961)= 3(4096 - 1)
=3(4095)= 3(4095)
=12285= 12285
Answer: 1228512285

9. Find the sum of the first 6 terms of the GP: 10, -20, 40, -80, ...
Solution: Using: Sn=a(rn1)r1S_n = \frac{a (r^n - 1)}{r - 1}
  • a=10a = 10,
  • r=2r = -2,
  • n=6n = 6.
S6=10((2)61)21S_6 = \frac{10((-2)^6 - 1)}{-2 - 1}
=10(641)3= \frac{10(64 - 1)}{-3}
=10(63)3= \frac{10(63)}{-3}
=210= -210
Answer: 210-210

10. The sum of the first 4 terms of a GP is 1875. The first term is 5, and the common ratio is 5. Find S4S_4.
paragraph
Solution: Using: Sn=a(rn1)r1S_n = \frac{a (r^n - 1)}{r - 1}
  • a=5a = 5,
  • r=5r = 5,
  • n=4n = 4.
S4=5(541)51S_4 = \frac{5(5^4 - 1)}{5 - 1}
=5(6251)4= \frac{5(625 - 1)}{4}
=5(624)4= \frac{5(624)}{4}
=31204= \frac{3120}{4}
=780= 780
Answer: 780780

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Thank you for taking the time to read my blog post! Your interest and engagement mean so much to me, and I hope the content provided valuable insights and sparked your curiosity. Your journey as a student is inspiring, and it’s my goal to contribute to your growth and success.
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If you found the post helpful, feel free to share it with others who might benefit. I’d also love to hear your thoughts, feedback, or questions—your input makes this space even better. Keep striving, learning, and achieving! 😊📚✨
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