Question

某次数学竞赛,共20题,答对一题得5分,不答或答错一题不仅不给分,还扣3分,小明得了84分,他答对几题?

Answer 1

设他答对 x 题,则

5x - 3(20 - x) = 84

5x - 60 + 3x = 84

5x + 3x = 84 + 60

8x = 144

x = 144÷8

x = 18

答：他答对 18 题.