Question

For an A.P t1 = 5 and t20 = 45 find S20​

Answer 1

Answer:

Value of S20 is 500

Step-by-step explanation:

let, common difference is d

t1 = 5 and t20 = 45

Hence, 5+(20-1)d = 45 => 5+19d = 45 => 19d = 40 => d =40/19

S20 is sum of th first 20 terms

Hence, S20 = 20/2 {10 + (20-1)×40/19 } = 10{10 + 40} = 10×50 = 500