Ex.11 .
The average age of a class of 39 students is 15 years. If the age of the
teacher be included, then the average increases by
3 months. Find the age of the teacher.
Sol. total age of 39 persons = (39 x 15) years = 585 years.
Average age of
40persons = 15 years 3 months = 61 / 4 years.
Total age of 40
persons = (61 / 4 x 40) years = 610
years
Age of the
teacher ( 610 – 585) years = 25 years
Ex. 12. The average weight of 10 oarsmen in
a boat is increased by 1.8 kg when one of the crew, who weighs 53 kg is
replaced by a new man. Find the weight of the new man.
Sol. total
weight increased = (1.8 x 10 ) kg = 18 kg.
Weight
of the new man = (53 + 18) kg = 71 kg.
Ex.
13. There were 35 students in a hostel. Due to the admission of 7 new students
the expenses of the mess were
increased by Rs. 42 per day while the average expenditure per head diminished
by Rs. 1. What was the original expenditure of the mess?
