There were 40 tons of coal in the warehouse. After a week, the amount of coal decreased by 20%.

There were 40 tons of coal in the warehouse. After a week, the amount of coal decreased by 20%. And a week later it increased by 20%. How many tons of coal were in the warehouse.

1) Let’s calculate 20% of the initial amount of coal in the warehouse and find out by how many tons of coal there is less coal after a week:

40: 100 * 20 = 0.4 * 20 = 8 t.

2) Let’s calculate how many tons of coal became in the warehouse in a week:

40 – 8 = 32 t.

3) Find 20% of 32 tons and determine by how many tons the amount of coal in the warehouse increased after another week:

32: 100 * 20 = 0.32 * 20 = 6.4 t.

4) Find out how many tons of coal were finally in this warehouse:

32 + 6.4 = 38.4 t.

Answer: Finally, there were 38.4 tons of coal in the warehouse.