what is the area of a rectangular surface that has length x feet and width y feet?
1, y is the reciprocal of x
2,the perimeter of the rectanggular surface is 5 feet
答案居然是A，不解
求NN帮助作者: davidliuscu 时间: 2011-9-16 21:27
还有一道：
If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?
