Question

An AP consists of 37 terms . The sum of the three muddle most terms is 225 and the sum of the least three terms is 429. Find the AP .

Answer 1

N=37
Middle term=37+1/2
=38/2
=19
Three middle most terms are
a18+ a19+ a20=225
a+17d+a+18d+a+19d=225
3a+54d=225
a+18d=75--------i
Now again,last three terms
a+34d+a+35+a+36=429
3a+105d=429
a+35d=143--------ii
By Solving equations i and ii, we get
-17d= -68
d= 4
Now find the value of a by putting value of d in equation i or ii...nd find the ap