Given: Out of 20 boys 6 are each of 1 m 15 cm height 8 are of 1 m 10 cm height And rest of 1 m 12 cm Formula Used: Average = Sum of observations/ Total number of observations Calculation: We have 1 m = 100 cm 6 boys are of 115 cm, 8 are of 110 cm. Rest boys = 20 - (8 + 6) = 6 boys ⇒ Other 6 boys are of 112 cm Average height =
6×115+8×110+6×112
20
=
(690+880+672)
20
⇒ Average height =
2242
20
⇒ 112.1 cm ∴ The average height of all of them is 112.1 cm.