How many terms are there in the A.P. 20, 22, 24, 26,…100?

Explanation

Let the number of terms be n.
Given , `a_(n) = 100, a = 20, d = 2 `
we have to find n.
Since `a_(n) = a + (n - 1)d`
`therefore 100 = 20 + (n- 1) xx2`
`rArr 80 = (n- 1) xx2`
`rArr n - 1= 40 `
`rArr n = 41 `
Hence required number of terms = 41