2(x) + 3(y) = 13, the sum of x + y = 7, solve for x and y

An an average person has 6×10 by the power of two as many red blood cells as white blood cells a small sample of the blood has 7×10 by the power of three white blood cells about how many red blood cells are in the sample

Two numbers have a sum of -19. one number is x. what expression represents the other number?

1. if events a and b are non-overlapping events, how do you find the probability that one or the other occurs? 2. what does it mean if p(a or b) equals 1?