1试卷共30道,答对1道得3分,答错1道扣1分,全做,共得78分,答对几道?(方程解答)

问题描述:

1试卷共30道,答对1道得3分,答错1道扣1分,全做,共得78分,答对几道?(方程解答)

设答对x道,则打错30-x道
则3*x-1*(30-x)=78
求得x=27
答:答对27道.