Question

in an A. P the sum of first 10 term is 285 and sum of first 20 is 870 find the sum of first 30 term​

Answer 1

S(10)=5{2A+9d}=285
2A+9d=57 ——-1
S(20)=10{2A+19d}=870
2A+19d=87 ———2
Therefore d=3 and A=15
S(30)=15{30+87}=1755