Question

Arithmetic Sequence Need Assistance

Answer 1

let the first term is
`a`

by the sum of first n term formula

`(20)/(2)(2a+19d)=25a</p><p>\\20a+190d=25a15</p><p>\\190d=5a</p><p>\\a=38d`

substitute to sum of first 30 term

`(30)/(2)(2a+29d)=(30)/(2)(2(38d)+29d)</p><p>\\=15(76d+29d)</p><p>\\=15(105d)</p><p>\\=1575d`