Question

The average or mean of three numbers is 10. The first two numbers are 10 and 4. What is the third number?

Answer 1

The third number is 16.
This is because to get the mean of 10 in 3 numbers the number should at up to 30.
a+b+c
10+4+c
14+c
30 - 14 = c
c = 16

Answer 2

The three numbers add together equal 10×3 or 30
which mean:
a+b+c=30
10+4+c=30
14+c=30
c=16. As a result, the third number is 16. Hope it help!