5. Determine the smallest natural number divisible by 15, whose digits are 0 or 4.

Tasks worth 10 points:
5. Since $15=3 \cdot 5$, the number must be divisible by both 3 and 5.

$1 \text{POINT}$

Divisibility by 5 implies that the units digit is 0.

$1 \text{POINT}$

Divisibility by 3 and the requirement for the smallest number give three digits 4.

The desired number is 4440.

2 POINTS

TOTAL 4 POINTS