If 0 < x < 1 and 0 < y < 1, which of the following must be true?
a. xy> 0
b. xy < 0
c. x/y < 0
d. x-y > 0
e. x-y < 0
i found out the answer is a, but there was no description to it. if someone could explain what they did to solve it and what number they used to plug in that would .

0<x<1 and 0<y<1

x>0 so x is positive and y>0 so y is also positive.
When you multiply two positive numbers you always get a positive number, so the product of x and y must be positive, or greater than 0.
xy>0 - it must be true
xy<0 - it can't be true
Also when you divide a positive number by a positive number you always get a positive number, so the quotient of x and y must be positive.
x/y<0 - it can't be true
D and E can be true, but don't have to. It depends on the values of x and y. If x>y, then x-y>0 is true and x-y<0 isn't true; if x<y, then x-y>0 isn't true and x-y<0 is true.

Therefore, only A must be true.