The average of five numbers is The number which should be included to make the average 12 is:

The correct answer is (a).

The average of five numbers is 12. This means that the sum of the five numbers is 60. To make the average 12, we need to add 12 to the sum of the five numbers. This means that the number that should be included is 12.

Option (b) is incorrect because 18 is greater than 12. If we add 18 to the sum of the five numbers, the average will be greater than 12.

Option (c) is incorrect because 22 is greater than 12. If we add 22 to the sum of the five numbers, the average will be greater than 12.

Option (d) is incorrect because 24 is greater than 12. If we add 24 to the sum of the five numbers, the average will be greater than 12.