Examples
Example 1. A batsman has a certain average runs for 16 innings. In the 17th inning he made a score of 85 runs thereby his average is increased by 3. What is his average after 17th inning?
Sol: The average for 17th inning has been increased by 3.
The total increase in the runs for 17th inning = 17 × 3
= 51
But the batsman scores 85.
Average runs in his 16th innings = 85 – 51
= 34.
Hence the average of runs after 17th innings = 34 + 3
= 37
Example 2. A man has 7 children. When their average age was 12 years, the child who was 6 years of age, died. What was the average age of surviving children 5 years after the death of the above child?
Sol: Average age of 7 children = 12 years
Total age of 6 children = 12 × 7 = 84 years
Total age of 6 children after the death of a child aged 6 years = 84 – 6 = 78
Hence the average age of the surviving children = 
After 5 yrs. = 13 + 5 = 18 yrs.
Example 3. If the weights of 5 students of a class are 49.6 kg, 39.8 kg, 45.2 kg and 24.6 kg respectively then what is their average weight?
Sol: Total weight of 5 students = 49.6 + 39.8 + 40.8 + 45.2 + 24.6
= 200 kg.
∴ Their average weight = 200/5
= 40 kg.
Example 4. The average temperature for Monday, Tuesday and Wednesday was 36°C . The average temperature for Tuesday, Wednesday and Thursday was. If the temperature for Thursday was 37°C, what was the temperature on Monday?
Sol: ∵ Average temperature for Monday, Tuesday and Wednesday = 36°C
Total temperature for Monday, Tuesday and Wednesday = 36 × 3
= 108°C
∵ Average temperature for Tuesday, Wednesday and Thursday = 38°C
∴ Total temperature for Tuesday, Wednesday and Thursday = 38 × 3
= 114°C
∴ Total temperature for Tuesday and Wednesday only = 114 – 37
= 77°C
∴ Temperature for Monday only = 108 – 77
= 31°C
Example 5. A train covers the first 16 km at a speed of 20 km per hour another 20 km at 40 km per hour and the last 10 km at 15 km per hour. Find the average speed for the entire journey.
Example 6. A vehicle travels from A to B at the speed of 40 km/hr, but from B to A at the speed of 60km/hr. what is its average speed during the whole journey?
Sol: Let the distance from A to B be x km
Example 7. The average age of a class of 40 boys is 16.95 years. A new boy joins the class and the average age now is 17 years. What is the age of the new boy?
Sol: The average age of 40 boys = 16.95 years
∴ Total are of 40 boys = 16.95 × 40
= 678 years
The average age of 41 boys = 17 years
∴ Total age of 41 boys = 17 × 41
= 697 years
∴ Age of the new boy = 697 – 678
= 19 years
