Average mark in Math in a class of 40 students is 45. Average mark of all the 30 boys is 48. Then the average mark obtained by the girls is:

Question: Average mark in Math in a class of 40 students is 45. Average mark of all the 30 boys is 48. Then the average mark obtained by the girls is:

Solution:
Average mark of 40 students is 45
Total mark of 40 students is (45 × 40)
= 1800

Average mark of all the 30 boys is 48
Total mark of all the 30 boys is (48 × 30)
= 1440

∴ Total marks of all the 10 girls is (1800 - 1440) = 360
The average mark of all the 10 girls is 360/10 = 36