In a rectangular coordinate system, a triangle is formed by vertices $A(5,3)$, $B(-1,4)$, $C(x,y)$. If the centroid of this triangle is $(4,2)$, find the value of $x-y$.
Given a square. Wendy draws 4 semi-circles quarters whose diameters are the sides of the square as follows. If the area of the shaded region is $8\pi-16$, find the area of the white region.
Numbers are drawn from 2000 integers 1 to 2000. At least how many numbers are drawn at random to ensure that there are two numbers whose product is 3600?
There are 3 black balls and 2 white balls. If 5 balls are drawn randomly one by one without replacement, find the probability that the 2nd one is a white ball.