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 ? ​

Answer 1

Answer:

8

Step-by-step explanation:

put the formula

Sn = n/2 [2a +(n-1) d]

put the values

a quadratic eqn. will b form

solve it

get 2 ans.

1) -15/2

2) 8

ans. can't be -ve so 8 will be the answer