Question

Find the sum of the following

102, 97, 92, … up to 27 terms.

Answer 1

Here a = 102, d = 97 – 102 = – 5

n = 27

S_n = `"n"/2` [2a + (n – 1)d]

S₂₇ = `27/2` [2(102) + 26(– 5)]

= `27/2` [204 – 130]

= `27/2` × 74

= 27 × 37 = 999

S₂₇ = 999