Question

The average height of a class of 30 students is 166 cm. The average height of the girls in the class is 158 cm and the average height of the boys is 170 cm. Find the number of boys in the class.

Answer 1

Answer:

20

Step-by-step explanation:

let no of boys be x and girls be 30-x

then avg=sum of all height/total no

so 166=sum /30

therefore sum=166 ×30=4980...eq1

now let us find sum of heights of all girls=

sum/total no=avg

no we hve taken as 30-x

so it becomes sum /30-x=158

sum =158×(30-x)=4740-158x.....eq2

find sum of heights of all boys

sum /total = avg

sum/x=170

sum = 170x...eq3

if we add eq2 and eq3 we can get eq 1 so

eq1=eq2 + eq3

4980=4740-158x+170x

4980-4740=170x-158x

240=12x

x=240/12=20

therefore there are 20 boys in the class