We seek an arithmetic series of 5 terms with common difference d=4 such that S5 = 100 Sn =[2a1 + (n-1)d] S5 = [2a1 + (5-1)(4)] 100 = [2a1 + (5-1)(4)] Multiply through by 2 200 = 5[2a1 + (4)(4)] 200 = 5[2a1 + 16] 200 = 10a1 + 80 120 = 10a1 12 = a1 Answer = 12+16+20+24+28 = 100 Edwin