Question

There is a bag with only red marbles and blue marbles.

The probability of randomly choosing a blue marble is 5/8.
There are 72 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 must be 27 red marbles

Explanation:

The probability of choosing a blue marble is 5/8,

This means that 5/8 of the marbles in the bag are blue marbles or,

Blue marbles = (Probability for a blue marble)(Total marbles)\

Now, total marbles = 72, and probability = 5/8,

so we get,

Blue marbles = (5/8)(72)

Blue marbles = 45

Hence there are 45 blue marbles,

To find the red marbles, we subtract the number of blue marbles from the total marbles,

Red marbles = 72 - 45

Red marbles = 27

There are 27 red marbles