In an examination average marks obtained by girls of a class is 85 and average marks obtained by boy

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In an examination average marks obtained by the girls of a class is $85$ and the average marks obtained by the boys of the same class is $87 .$ If the girls and boys are in the ratio $4: 5,$ average marks of the whole class $(approx.)$ is closest to

A

$85.9$

B

$86.5$

C

$86.4$

D

$86.1$

Solution

Ratio of $G: B$

$4: 5 \Rightarrow 4 x, 5 x$

Average mark of whole class $=\frac{85 \times 4 x+87 \times 5 x}{9 x}$

$=\frac{340 x+435 x}{9 x}$

$=\frac{775 x}{9 x}$

$\simeq 86.1$

Standard 13

Quantitative Aptitude

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