Question

There is a bag with only red marbles

and blue marbles.
The probability of randomly choosing
a blue marble is
7/9
There are 63 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

14 red marbles.

Explanation:

If I am reading this correctly, since the probablitly of choosing a blue marble is 7/9, then 7/9 of the bag must be blue marbles. That amounts to 7/9*63=49 and the bag containing 49 blue marbles. Therefor, 63-49=14 is the number of red marbles in the mag.