The mean of 3 numbers is 20. Two of the numbers are 21, and 35. What is the 3rd number?

The mean of 3 numbers is 20. Two of the numbers are 21, and 35. What is the 3rd number?

The mean of 3 numbers is the sum of 3 numbers divided by 3. Let the 3rd number be n. We have:
Mean = (21 + 35 + n) / 3

The Mean is given as 20, so we have:
20 = (n + 56) / 3

Cross multiply:
n + 56 = 20 * 3
n + 56 = 60

To solve for n, we type this number in our search engine and we get:
n = 4