The mean of four numder is 30. if three of the numbers are 12, 50, and 48, what is the fourth number

If the mean of 4 numbers is 30 then that means that the total of all the numbers added together must add up to 120 (30 x 4)

then you subtract the three numbers that you have from the total

120-12-50-48 = 10

so the last number is 10