d Word Problems 7 & 8 | Job Exam Rare Mathematics (JEMrare) - Solved MCQs

# Word Problems 7 & 8

Problem 7: There are 40 boys in a class. One of them weighing 100 lbs goes away, a new boy joins the class at the same time. The average weight of the boys is thus increased by 1/4 lbs, Find the weight of the new boy.

Solution:

Suppose there are 39 boys in class whose weight is x1,x2,x3 ………x39 and one boy (40th) has wieght of 100lb.

So their average weight is ‘y’ then;

Now suppose 100lb boy leaves away and new boy comes whose weight is ‘zlb’

Then again average weight of 40 including new boys is calculated as;

Put values of x1+x2+x3+……..+x39 from eq (1) above, we get;

But ,

So,

Or

So, the weight of new boy is 110 lb

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Problem 8: The average age of a class of 20 boys is 14.95 years. The avaerage age of the class is raised to 15 years by the arrival of a new student. How old is that new boy?

Solution:

Let’s suppose  ages of 20 students be x1,x2,x3………………..x20

Then average age of 20 students is obtained by taking sum of their ages and dividing the sum by number of student i-e20;

But average of 20 students is given to be 14.96 in statement;

Let new boy’s age is ‘y’ years

Now average age of total 21 boys is given by;

But average age of 21 students is given to be 15 years

Put value of x1+x2+x3+…….+x20   here;

So, the age of new boy is 16 years

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