1.

3.In an AP:0 given a 5, d 3, a, 50, find n and S,PM/2

Answer»

We have, a= 5, d=3 and an=50

> a+(n-1)d= 50

> 5+(n-1)3=50

> 3(n-1)=50-5

> n-1 = 45/3

> n-1 = 15+1 = 16

Putting n = 16, a= 5 and l = an = 50 in Sn= n/2(a+l),We get

S16 = 16/2( 5 + 50) = 8 × 55 = 440

Hence, n= 16 and S16 = 440


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