Brad has made two discs for a game.
These discs should have numbers on each side but one of the numbers is missing.
When Brad flips the discs and adds the numbers that he can see, he wants to get only sums of 8, 10, 11 or 13.
What does Brad need the missing number to be?
Solution:
At the moment Brad can get 4 and 4 to make 8, or he can get 4 and 6 to make 10. He also needs to be able to get totals of 11 and 13.
The missing number will be able to add onto either the 4 or the 6 on the first disc.
If you add 7 to 4 you get 11 and if you add 7 to 6 you get 13. The missing number must be 7.
Extension:
Try changing the 4 on disc 2 to a different number. Can you then find a number for the other side of the disc that will work?