4道PrepMath题求教?

Wdrrrrrrr

之前发图片发现回帖率不是很高 可能不太方便读题 所以还是手打题目吧 希望各路高人不吝赐教 为了不先入为主 答案回复可见

1.If M is a positive integer, then M^2 has how many digits?
(1)M has 3 digits
(2)M^2 has 5digits


2.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 the last 2 flips?


3.A string of 10 lighrbulbs is wired in such a way that if any individual lightbulb fails, the entire string fails. If for each individual lightbulb the probability of failing during time period T is 0.06, what is the probability that the string of lightbulbs will fail during time period T




4.If X^3y^4=5000, is y=5?
(1)y is a positive integer
(2)x is an integer
     答案：E  1/8  1-0.94^10  C