Here are five cards. 1 5 7 9 11 One of the cards is removed. The mean of the numbers on the remaining four cards is 6 Which card was removed
If four cards average 6, then they must total 24.
18 & 6 will do it, so the removed card was the 9. (18=7+11 and 6=5+1)
.
+1678 
