Question

There are 50 students in a class in which 40 are boys and rest are girls. The average weight of the class is 44 kgs and the average weight of the girls is 40 kgs. Find the average weight of the boys.

Answer 1

We have
n = No., od students in a class = 50
n₁ = No., of boys in a class = 40
n₂ = No., of girls in a class = 10
`bar"X"_1` = Average weight of boys = ?
`bar"X"_2` = Average weight of girls = 40 kgs.
∴ `bar"X" = ("n"_1 bar"X"_1 + "n"_2 bar"X"_2)/("n"_1 + "n"_2)`
⇒ 44 = `(40bar"X"_1 + 10 xx 40)/(40 + 10)`
⇒  50 x 44 = `40bar"X"_1 + 400`
⇒  2200 = `40bar"X" + 400`
⇒  `40bar"X"_1` = 1800
⇒  `bar"X"_1` = 45
Hence, the average weight of boys is 45 kgs.