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WAEC Mathematics 2020 Paper

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Question : 11

Total: 48

The first term of a geometric progression (G.P) is 3 and the 5th term is 48. Find the common ratio.

2
4
8
16

Solution:

Concept:

In a geometric progression, the

n

th term is given by

T_n = ar^{n-1}

, where

a

is the first term and

r

is the common ratio.

Explanation:

Given: first term

a = 3

and 5th term

T_5 = 48

.

Using the formula,

T_5 = ar^{4}

.

So,

48 = 3r^{4}

.

Divide both sides by 3:

r^{4} = \frac{48}{3} = 16

.

Since

2^4 = 16

, we get

r = 2

.

Thus, the common ratio is

2

.

Answer:

A. 2

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