Problema Solution

There are 10 marbles in a bag, and the marbles are either red or blue. Eric will randomly choose two marbles from the bag, without replacing the first one. If the probability of both marbles' being red is

2

15

, how many BLUE marbles are in the bag?

Answer provided by our tutors

Let x represent the number of red marbles in the bag, x>0


10 - x is the number of blue marbles in the bag


the probability that 2 marbles are red is:


P(2 marbles are red) = x(x-1)/(9*10)


x(x-1)/(9*10) = 2/15

........


click here to see all the equation solution steps


........

x = 4 red marbles


10 - x = 10 - 4 = 6 blue marbles


There are 6 blue marbles in the bag.