Average age of three boys is 15 year. If ratio of their ages is 3:5: 7, age of oldest boy in year ?

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The average age of three boys is $15$ $year.$ If the ratio of their ages is $3:5: 7,$ what is the age of the oldest boy in $year$?

A

$7$

B

$14$

C

$20$

D

$21$

Solution

Total age of all the three boys $=3 \times 15=45$ years

Given ratio of ages $=3: 5: 7=\frac{7}{3+5+7} \times 45=21$ years

Standard 13

Quantitative Aptitude

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