The mean of four numbers is 18 . If one of the four numbers is removed, the mean of the three remaining numbers is 17 . What is the value of the number that was removed?

To find the number that was removed, we can start by using the information given about the means. The mean of the four numbers is 18, which means the total sum of the four numbers is: \[ 4 \times 18 = 72. \] When one of the numbers is removed, the mean of the remaining three numbers becomes 17, which means their total sum is: \[ 3 \times 17 = 51. \] Let \( x \) be the number that was removed. We can set up the equation: \[ 72 - x = 51. \] Now, solving for \( x \): \[ x = 72 - 51 = 21. \] So, the value of the number that was removed is 21.