求助两道prep的DS题。。数学还是不行啊。。。

两道均为DS题：

A store purchased 20 coats that each cost an equal amount and then sold each of the 20 coats at an equal price. What was the store's gross profit on the 20 coats?

(1)If the selling price per coat had been twice as much, the store's gross profit on the 20 coats would have been $2400.

(2)If the selling price per coat had been &2 more, the store's gross profit on the 20 coats would haveIf  been &440.

答案是D

为什么（1）也可以呢？

If d is a positive integer and f is the product of the first 30 positive integers, what is the value of d?

(1)10^d is a factor of f

(2)d>6

答案是C

怎么做呢。。。。。

第一题我想A的意思是出售的价格是成本的两倍吧

第二题，我的算法有点复杂，把30个数中有2个5的因子都提出来，得到2有23个，5有7个， 那单单1的不出，因为有很多可能性，加上条件2就可以得出D=2的7次方×5的七次方，不知道有没有简便的办法，请NN指教

再顶下，我今天做prep又碰到第一题了。。。可是这次的答案是B，有没有人也做过这题啊。。。答案到底是什么呢？