If two of the four expressions x+y,x+5y,x-y,5x-y are chosen at random, what is the probability that their product will be of the form of x^2-(by)^2.
a)1/2
b)1/3
c)1/4
d)1/5
e)1/6

Q2.For any positive integern, the length of n is defined as the number of prime factors whose product is n. For example, length of 75 is 3, since 75=3*5*5. How many two-digit positive integers have length 6.
a)None
b)One
c)Two
d)Three
e)Four