When a fifth of the class is absent, there are 24 pupils present. What is the total number of pupils in the class?

Since 1/5 of the class is absent, this must mean that 4/5 of the class is present. We are told that 24 pupils are present, so 4/5 of the class must equal 24 pupils. Now we need to find out how many pupils 1/5 of the class equals. If 4/5 of the class equals 24 pupils, then 1/5 must equal 24 divided by 4. This is because 4/5 divided by 4 is 1/5. Therefore, 1/5 of the class must equal 6 pupils. We then add 6 to 24 to get 30, since 4/5 + 1/5 = total number of pupils in the class.

Answer: There are 30 pupils in the whole class.