Hello, fahad!

Here are #4 and #5 . . .

(3) Find the sum of first 100 terms of the given arithmetic sequence: -17,-12,-7,-2, 3, ...

The sum of the first n terms is: .Sn .= .½n[2a + (n-1)d]

We have: .a = -17, d = 5, n = 100

Therefore: .S100 .= .½(100)[2(-17) + 99(5)] .= .23,050

(4) Find thenth term of the geometric series if a = 125/8 , r = 2/5 , n = 8

Thenth term is: .an .= .a·r^{n-1}

Therefore: .a8 .= .(125/8)(2/5)^7 .= .16/625