[求助]请教两道math题

popandcatUID: 114719

管卫东的那本书里的，P20,  P21

1.If a motorist had driven 1 hour longer than on a certain day and at an average rate of 5 miles per hour faster, he would have

covered 70 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) can not be determined

5. A jewelry dealer initially offered a bracelet for sale at an asking price that would give a profit to the dealer of 40 percent of the original cost. What was the original cost of the bracelet?
(1) After reducing this asking price by 10 percent, the jewelry dealer sold the bracelet at a profit of $403.
(2) The jewelry dealer sold the bracelet for $1,953.

For the first quesiton, the answer in the book is E.  I want to choose D.
for the second quesiton, the answer in the book is A.  I am not sure. Is it because there is no mention of the relationship between the asking price and $1,953?
Are the anwers in the book both right? If so, can anyone explain them for me? Lots of thanks!

stephanie_sisuUID: 201114

第一题选D
解答如下
设原速度为v，路程为s，时间为t
则可得到两个方程
vt=s
(v+5)(t+1)=s+70
联立两式，可得到 vt+5t+v+5=vt+70  => 5t+v=65
所求的是 (v+10)(t+2)=vt+2(5t+v)+20=?
根据已经推断得到的等式，可以知道 vt+2(5t+v)+20=vt+130+20=vt+150
所以为D

stephanie_sisuUID: 201114

第二题，好像根据条件B也可以解答的……汗……
所以答案是不是有问题……飘走……

popandcatUID: 114719

原帖由 stephanie_sisu 于 2006-5-20 18:53 发表
第二题，好像根据条件B也可以解答的……汗……
所以答案是不是有问题……飘走……

其实如果说第二个错的话，那原因只能因为这个价格“$1,953”与asking price的关系不请，有可能是asking price 的变化后的价格。还是不太确定。。。