To get an average of two or more quantities divide the sum of these quantities
by the total number of the quantities.

Example:
A three-sided figure has sides 6cm, 3cm and 6cm.
What is the average length per side of the figure?
Answer: Add all three sides: 6cm + 3cm +6cm = 15cm.
Divide by the number of sides: 15cm : 3 = 5cm.
The average length per side is 5 cm.

Solve:

1.
Jim is 12 years old. His sister is twice younger. His mother is 3 times
older than Jim. Jim's father is 6 years older than Jim's mother. How
old are Jim's sister, mother and father?

What is their average age?

3.What is the average number of students in each class if there are
250 students in 10 classes?

2.
One of the two movies has a length of 2 hours and 15 minutes.
The average length of the two movies is 1 hour and 45 minutes.
What is the length of the second movie?

Hint: 1 hour has 60 minutes.

4.
The height of three basketball players is 210 cm, 220 cm and 191 cm.
What is their average height?