Question

In an A.P., the first term is 1 and the common difference is 4. How many terms of the
A.P. must be taken for their sum to be equal to 120?
(A) 6
(B) 7
(C) 8
(D) 9​

Answer 1

given that a=1 and d=4 ,sum of n terms is 120....

by substituting the given values in the formula ,,we got two values for n ,since n is a non negative integer,n=8

so your answer is 8::)