A big container contains 7 marbles while a small container contains 4 marbles. There are 11 containers and 62 marbles altogether. How many small containers are there?

1. Assume all containers are big and calculate the total number of marbles

Assume all $11$ containers are big containers.
Total marbles $= 11 \times 7 = 77$

2. Find the difference between the assumed total and the actual total

Difference in total marbles $= 77 - 62 = 15$

3. Find the difference in marbles between one big and one small container

Difference per container $= 7 - 4 = 3$

4. Calculate the number of small containers

Number of small containers $= 15 \div 3 = 5$