First write down all the pairs whose coins add up to the target.
Usually two pairs fit. Then work out the favor for each pair.
Starting favor minus the cost of both decisions: only one pair stays high enough.
Example
For parents
What does this exercise practice?
The council decision trains checking two conditions at once. The first one leaves several options open, only the second decides.
Common pitfalls
Many children stop after the coins add up. The favor still has to be checked though.
How to practice at home
Set two goals, for example pocket money and screen time. Which two spendings fit both?