Question

2. The first and last term of an AP are 1 and 121 respectively. If the sum of the

series is 671, find a) the number of terms in) in the AP b) the common
difference between them.​

Answer 1

Explanation:

since you provided 1st and the last terms

the equation can be nth term

n/2 × ( a + l) = nth sum

n/2 × ( 1 + 121) = 671

n/2 × 122 = 671

61 n = 671

n = 11

a) so there are 11 terms

then,

so as 11th term is 121

let's find common diff

a + ( n-1) d = nth term

1 +( 11-1) d= 121

10d = 121 -1

10d = 120

common difference = 12