Upin and Ipin went fishing. They took their fathers along (Upin and Ipin are not brothers), and nobody else.
Upin and his father caught the same number of fishes. Ipin caught three times as many fishes as his father. Altogether they caught 25 fishes. How many fishes did Upin caught?
Please answer in comment below.
(Note: There is an answer. A reasonable one. The usual assumptions hold: every fish has one catcher, one cannot catch a fraction of a fish, etc.)
Source: I read this in a journal article written by Andy Liu. But it sounds like math folklore.