Question

There is a bag with only red marbles and blue marbles. The probability of randomly choosing a red marble is 3/10. There are 12 red marbles in the bag and each is equally likely to be chosen. Work out how many marbles in total there must be.

Answer 1

40

Explanation:

Let x = total number of marbles

p(red) = (number of red marbles)/(total number of marbles)

3/10 = 12/x

3x = 120

x = 40

Answer: The total number of marbles is 40