Averages Part 4

Problem 1: The average age of class A and Class B is 11 years, the average age of class A is 8 years and the average age of class B is 15 years. If the number of students in class A is 52. Then find the number of students in class B?

Solution:

8*52 + 15*B =(52+B)*11

8*52 +15B = 52*11 +11B

4B=52(11-8)

B=39

Problem 2: The average of 20 numbers is 25. If one of the numbers is considered as 35 instead of 75, what will be the new average?

Solution:

25+\frac{35-75}{20}

25-\frac{40}{20}=23

Problem 3: The Average age of A and B is 50 years and that of B and C is 38 years. What is the difference between the age of A and C?

Solution:

A+B = 50*2 =100

B+C = 38*2 = 76

A-C = 24

Problem 4: The average of 30 numbers is 20. The average of the first 12 numbers is 26. Find the average of remaining numbers?

Solution:

20-\frac{6\times 12}{18}=16

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