A fish weighs 10 pounds more than half its weight. How much does it weigh?

I think that guess and check is a reasonable way to approach this problem. Six pounds is a good size fish so start with a guess of 6 pounds.

13 pounds is larger than 6 pounds so the fish needs to be larger. Try 10 pounds.

15 pounds is larger than 10 pounds so the fish still ins't large enough. Try 30 pounds.

This time the fish is too large so try something between 10 pounds and 30 pounds.