可否讲下这道题

kun861010

If a motorist had driven 1 hour longer
on a certain day and at an average rate
of 5 miles per hour faster, he would
have covered 70 more miles than he
actually did. How many more miles
would he have covered than he
actually did if he had driven 2 hours
longer and at an average rate of 10
miles per hour faster on that day?
(A) 100 (B) 120 (C)
140
(D) 150 (E) 160

这个不是第一次碰到了,多行了5MILES一个小时,怎么会COVER70MILES呢?请大家指教.

zhangfei3322

不是covered 70 miles 而是covered 70 more miles ，设原速度，时间，路程分别是v，t，s，所求为x

vt=s        

(v+5)(t+1)=s+70

(v+10)(t+2)=s+x

前两个相减v+5t=65,后两个相减2v+10t+20=x，带入x=150