Question

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

The probability of randomly choosing a red marble is 5/8.
There are 25 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

• 65 marbles

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Let the number of red marbles be 5x, then the total number of marbles is:

• 5x + 8x =
• 13x

Since we have 25 red marbles, the value of x is:

• 5x = 25
• x = 5

Total number of marbles is:

• 13*5 = 65