Four fathers wanted to sponsor a skiing trip for their children.

The first promised: "I will give 11500 CZK,"

the second promised: "I will give a third of what you others give in total,"

the third promised: "I will give a quarter of what you others give in total,"

the fourth promised: "And I will give a fifth of what you others give in total."

How many crowns did the second, third, and fourth fathers promise?
The second father contributed a third of what the others did, which amounted to a quarter of the total contribution. (If we denote his contribution by $x$, the others contributed $3x$. If the total amount is $p$, then $x + 3x = p$, hence $x = \frac{p}{4}$.) Similarly, if the third father contributed a quarter of what the others did, he contributed a fifth of the total amount, and if the fourth father contributed a fifth of what the others did, he contributed a sixth of the total gift. Therefore,

$$
p = 11500 + \frac{p}{4} + \frac{p}{5} + \frac{p}{6}
$$

After rearrangement, we have $\left(1 - \frac{37}{60}\right) p = 11500$ Kč, so the total contribution $p$ was 30000 Kč. From this, it is easy to conclude that the second father contributed $\frac{p}{4} = 7500$ Kč, the third father contributed $\frac{p}{5} = 6000$ Kč, and the fourth father contributed $\frac{p}{6} = 5000$ Kč.

Note. If we denote the contributions of the second, third, and fourth fathers by $x$, $y$, and $z$ respectively, then the resulting values are the solutions to the following system of equations:

$$
x = \frac{1}{3}(11500 + y + z), \quad y = \frac{1}{4}(11500 + x + z), \quad z = \frac{1}{5}(11500 + x + y) \text{. }
$$