Binomial theorem

Question

The coefficients of the (r−1)th,rth and (r+1)th terms in the expansion of (x+1)n are in the ratio 1 : 3 : 5. Find n and r.
(Using tr/tr-1 = n-r+1/r)

Answer 1

⇒ 3 n − 8 r + 3 = 0 

Solving & n-4r+5=0 3n-8r+3=0 

n=7, r=3