To number the apartments in a building, metal plates with digits were used: one digit on each plate. How many plates were used to number 136 apartments in the building?

301 plates

Step-by-step explanation:

For numbers between 0 and 9, 1 plate was used each.

This means that 10 plates were used.

For numbers between 10 and 99, 2 plates were used for each.

This means that the number of plates used will be:

2 * 90 = 180 plates

For numbers between 100 and 136, 3 plates were used for each.

This means that the number of plates used is:

3 * 37 = 111 plates

The total number of plates used is therefore:

10 + 180 + 111 = 301 plates

301 plates were used in total.