Question

There is a bag with only red marbles and blue marbles. The probability of randomly choosing a blue marble is 59. There are 45 marbles in total in the bag and each is equally likely to be chosen. Work out how many red marbles there must be.​

Answer 1

There are 20 red marbles

Since the probability of randomly choosing a blue marble is 5/9, then the probability of choosing a red marble will be:

= 1 - 5/9

= 4/9

If there are 45 marbles in total, the number of red marbles will be:

= 4/9 × 45

= 20

Therefore, there are 20 red marbles.