Question

average height of 30 boys out of a class of 50 is 160 cms.if average height of the remaining boys is 165 cm, the average height of the whole class is

Answer 1

The formula of average is,

x̅ = ∑Xi / n

So Average height of 30 boys is 160 cms can be written as,

x̅ = ∑Xi / n

160 = ∑Xi / 30 ( i takes values from 1 to 30)

∑Xi = 4800 ( i takes values from 1 to 30)

The average height of the remaining 20 boys is 165 cm.

ӯ = ∑Yi / n

165 = ∑Yi / 20 ( i takes values from 1 to 20)

∑Yi = 3300

The average of the whole class is ,

Average = ( ∑Xi + ∑Yi ) / N

= ( 4800 + 3300) / 50

= 162 cm

The average height of the whole class is 162 cm