Question

what is the sum of first 10 terms and next 10 terms of arithmetic sequence 10 15 20 25​

Answer 1

a =10 , d = 5 (given)

Answer :

sum of first 10 terms = n/2 (2a + (n-1)d)

sum of first 10 terms = 10/2(2×10 + (10-1)5)

sum of first 10 terms = 5(20 + 45)

sum of first 10 terms =5(65) = 325

next 10 terms of arithmetic sequence are t5 ,t6,t7..t14

t5 = a+ 4d = 10 + 20 = 30

t6 = a+ 5d = 10 + 25 = 35

t7 = a+ 6d = 10 + 30 = 40

….t14 = a +13d = 10 + 75 = 85