Question

For an AP(arithmetic progression) if S49=100 and T50=25 then S50=____

Answer 1

now 
t50=25
a+49d=25
a=25-49d_ _ _ _ _ 1

now, 
s49=100

49/2[ 2(25-49d) + 48d]= 100
49[50-98d+48d]=200
2450-2450d
d=45/49

now putting this value in 1

a= 25 - 45
a= -20

now 

s50= 50/2[-40+45]
s50=125       - - - - - - -ans

Answer 2

sum of 50 terms in arithmetic progression is 125