Question

A bag contains 20 marbles: 4 red, 6 green, 5 white and 5 black. One marble is drawn. What is P(not picking a white)?

Answer 1

`15/20=3/4`

Explanation:

From our selection of 20 marbles, 15 aren't white (`20-5=15`). And so the probability of picking a non-white marble is:

`15/20=3/4`

We can also do this in a different way, by saying from the `20/20`, which is the odds of picking a marble of any colour from a sack of marbles and subtracting from that the odds of picking a white marble `(5/20)`:

`20/20-5/20=15/20=3/4`