21. When the young fishermen were asked how many fish each of them had caught, the first one answered: "I caught half the number of fish that my friend caught, plus 10 fish." The second one said: "And I caught as many as my friend, plus 20 fish." How many fish did the fishermen catch?
21. Let the second one catch $x$ fish, then the first one catches $\frac{1}{2} x+10$ fish. According to the second fisherman's statement, he caught $\left(\frac{1}{2} x+10\right)+20$ fish. We have the equation $x=\left(\frac{1}{2} x+10\right)+20$, from which $x=60$, i.e., the second one caught 60 fish. Then the first one caught $\frac{1}{2} \cdot 60+10=40$ fish, and together -100 fish.