MATHEMATICS

JAMB 2020 - Question 20

Mathematics 2020 JAMB Past Questions - Question 20: The first term of a geometrical progression is twice its common ratio. find the sum of the first two terms of the progression if its sum to infinity is 8.

Choose the most appropriate option for the gap .
The first term of a geometrical progression is twice its common ratio. find the sum of the first two terms of the progression if its sum to infinity is 8.
A:
B:
C:
D:
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Correct Answer

C

Explanation

s͚ = a/1 – r = 8……………….(1)a = 2r ……………………(2)sub (ii) into (i) i.e 2r /1-r = 82r = 8 – 8r10r = 8 r = 8/10 = 4/5 a = 2 X 4/5 = 8/5 ist term = 8/5 2nd term = 8/5 X 4/5 = 32/25Ist term + 2nd term , 8/5 + 32/25 = 40 + 32 /25 = 72 / 25

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