Question

if the sum of the n terms of two AP is n+7:3n+1,then find the ratio of 7th terms of the series

Answer 1

We know that
Sum of n terms = n(2a+(n-1)d)/2 
Now[tex] \frac{2a1+(n-1)d1}{2a2+(n-2)d2} = \frac{n+7}{3n+1} we need the ratio of 7th term . So put n=13 in the above equation [/tex]
$\frac{2a1+12d1}{2a2+12d2} = \frac{n+7}{3n+1}$
$\frac{a1+6d1}{a2+6d2}= \frac{n+7}{3n+1}$

Put n=13 in rhs also

[tex] \frac{a1+6d1}{a2+6d2} = \frac{13+7}{39+1} = \frac{20}{40}= \frac{1}{2} [/tex]

Answer 2

hey mate!! here is your answer