Thread: numbers + probability

What is the probability that a two digit number chosen at random will be a multiple of 3 and not of 5 .

Originally Posted by mathaddict

What is the probability that a two digit number chosen at random will be a multiple of 3 and not of 5 .

One way is just to write out all two digit numbers that are multiples of 3 and cross out those that are also a multiple of 5 .... How many are there ....? Now divide by the total number of two digit numbers.

Hello, mathaddict!

What is the probability that a two digit-number chosen at random
will be a multiple of 3 and not of 5?

There are 90 two-digit numbers.

One-third of them are mutliples of 3: . multiples of 3.

But every fifth one of them is a multiple of 5: . multiples of 15.

Hence, there are: . multiples of 3 which are not multiples of 5.


Therefore: .