3. Ivan collects 2-kuna and 5-kuna coins. He has collected 39 coins and now has 144 kuna. How many 2-kuna coins and how many 5-kuna coins does he have?
3. If all the coins were 2 kuna coins, the total would be $39 \cdot 2=78$ kuna.

1 POINT

To reach 144 kuna, there is still $144-78=66$ kuna missing.

1 POINT

Each time a 2 kuna coin is replaced with a 5 kuna coin, the amount increases by 3 kuna. 1 POINT To increase by 66 kuna, 22 of the 2 kuna coins need to be replaced with 5 kuna coins because $22 \cdot 3=66$.

This leaves $39-22=17$ 2 kuna coins.

So, Ivan has 22 5 kuna coins and 17 2 kuna coins.

Note: If a student arrives at the correct solution through successive approximation, i.e., by trying different possibilities, they receive all 6 points. If a student has the correct solution without any procedure, they receive 4 points.