Question

The average height of 8 boys in a class is 168cm. When a ninth boy joins the group, the average height becomes 167cm. Find the height of the ninth boy.​

Answer 1

Answer:

average height of 8 boys= 168cm

sum of height of 8 boys= 168×8=1344 cm

average height of 9 boys= 167cm

sum of height of 9 boys= 167×9=1503 cm

height of 9th boy=1503-1344=159cm

please mark it as brainlist

Answer 2

Answer:  The required height of the ninth boy is 159 cm.

Step-by-step explanation:  Given that the average height of 8 boys in a class is 168 cm. When a ninth boy joins the group, the average height becomes 167 cm.

We are to find the height of the ninth boy.

Let h represents the height of the ninth boy and S represents the sum of the sum of the ages of the first 8 boys.

Then, according to the given information, we have

$\dfrac{S}{8}=168\\\\\Rightarrow S=168\times8\\\\\Rightarrow S=1344$

and

$\dfrac{S+h}{9}=167\\\\\\\Rightarrow \dfrac{1344+h}{9}=167\\\\\Rightarrow 1344+h=167\times9\\\\\Rightarrow 1344+h=1503\\\\\Rightarrow h=1503-1344\\\\\Rightarrow h=159.$

Thus, the required height of the ninth boy is 159 cm.