The mean of four number is 20. If one of the number is 15, what is the sum of the other number?

The sum of the remaining numbers is 65.

In order to tell this we first need to find the sum of the numbers in total. In order to do that, we can multiply the average by how many numbers we have.

4*20 = 80

Since we have a total sum of 80, we can now just subtract the aforementioned 15 to get the answer to your question.

80-15 = 65