Average of test scores of a class of 'm' students is 70 and that of 'n' students is

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The average of the test scores of a class of $'m'$ students is $70$ and that of $'n'$ students is $91.$ When the scores of both the classes are combined, the average is $80 .$ What is $n / m$ ?

A

$\frac{11}{10}$

B

$\frac{13}{10}$

C

$\frac{10}{13}$

D

$\frac{10}{11}$

Solution

Total score of a class of $m$ students $=70 \times m$

Total score of a class of $n$ students $=91 \times n$

$70 m + 91 n =( m + n ) 80 \quad 70 m +91 n =80 m +80 n$

$11 n =10 m \Rightarrow \frac{ n }{ m }=\frac{10}{11}$

Standard 13

Quantitative Aptitude

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