Here's a question that I couldn't solve, apparently:
The mean of four numbers is $12$. When the greatest number is removed, the mean of the remaining three numbers is $9$. What number was removed?
Thanks so much if you can solve it! PS: You probably can. LOL :)
If you know the mean and the number of terms, you know the sum (mean=sum/# of terms). From the first sentence, you find the sum of four numbers. In the second sentence you get the sum of the remaining three. Can you take it from here?