You have eight coins worth either 1 or 2 points each. Their total value is 13 points. How many 2-point coins do you have?
A little nudge?
Imagine all eight coins were worth just 1 point.
Ready for the answer?
Five 2-point coins.
Eight 1-point coins would total 8. You need 5 extra points, and replacing each 1-point coin with a 2-point coin adds exactly one. So five coins are worth 2 and three are worth 1.