Average:
Average= Sum of all quantities / number of quantities
Question:
The average age of 30 kids is 9 years. If the teacher’s age is included, the
average age becomes 10 years. What is the teacher’s age?
Total age of 30 children = 30 × 9 = 270 yrs.
Average age of 30 children and 1 teacher = 10 yrs
Total of their ages = 31 × 10 = 310 yrs
Teacher’s age = 310 – 270 = 40
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