The sum of $n$ term of $2$ A.P are in the ratio $(3 n + 8) : (7 n + 15)$ . Find the ratio of sum upto their $12^{t h}$ term.

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Solution

Sum of AP $= 2 a + (n -) d =$
Ratio of $2$ AP's $= \frac{3 n + B}{7 n + 15}$ for $n = 12$
$\Rightarrow \frac{3 \times 12 + B}{7 \times 12 + 15} = \frac{44}{99} = \frac{4}{9}$ .

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Similar questions

A . P

(3 n + 8); (7 n + 15)

12 t h

3 n + 8 : 7 n + 15

The ratio between the sum of n terms of two A.Ps is 3n + 8 : 7 n + 15. Then the ratio between their $12^{t h}$ terms is

n

(3 n + 8) : (7 n + 15) .

(i) 12 t h

(i i) 15 t h

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