In an examination average mark obtained by the girls of a class is 85 and the average mark 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

Given that, Average mark obtained by girls in a class = 85

and average mark obtained by boys in a class = 87

If number of boys & number of girls is considered as x & y respectively, given that x:y=4:5 => x= $$\frac{4y}{5}$$

Also, Sum of marks obtained by girls = 85x and sum of marks obtained by boys = 87y

Therefore,

Average of whole class = $$\frac{85x+87y}{x+y}$$

=$$\frac{85 \times \frac{4y}{5}+87y}{\frac{4y}{5}+y}$$

=86.1