Question

3. Average age of 5 boys is 13 yr. One more boy joins them and the average age becomes 12 yr. The age of the boy who joins last is
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Answer 1

Correct question:-

The average age of 5 boys is 13 years.One more boy joins them and the average becomes 12 years. The age of the boy who joins last is?

Given:-

→Average age of 5 boys=13 years

→When one more boy joins, the average becomes=12 years

To find:-

→Age of the boy,who joined last

Solution:-

We know that:-

=>Average=Sum of observations/No of observations

Here,number of observations is 5 and average is 13,then sum of observations:-

=>Sum of observations/13=5

=>Sum of observations=13×5

=>Sum of observations=65

Let the age of the boy,who joins last be x years.

Now,when another boy joins:-

•Sum of observations=65+x

•No of observations=5+1=6

•New Average=12

Thus:-

=>(65+x)/6=12

=>65+x=12(6)

=>65+x=72

=>x=72-65

=>x=7

Thus,age of the boy who joins last is 7 years.

Answer 2

Answer:

7

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