The mean of 5 numbers is 20. If one number is excluded, the mean of the remaining numbers becomes 23. What is the excluded number?
Answer: A
The sum of the original 5 numbers = Mean × Count = 20 × 5 = 100.
After one number is excluded, there are 4 numbers left, and their mean is 23.
The sum of the remaining 4 numbers = 23 × 4 = 92.
The excluded number is the difference between the original sum and the new sum.
Excluded number = 100 - 92 = 8.