Question

A school has 4 sections of Chemistry in class X having 40, 35, 45 and 42 students. The mean marks obtained in Chemistry test are 50, 60, 55 and 45 respectively for the 4 sections. Determine the overall average of marks per student.

Answer 1

Here n₁ = 40, n₂ = 35, n₃ = 45, n₄ = 42, `bar"X"_1 = 50, bar"X"_2 = 60, bar"X"_3 = 55 and bar"X"_4 = 45`.

∴ `bar"X" = ("n"_1bar"X"_1 + "n"_2bar"X"_2 + "n"_3bar"X"_3 + "n"_4bar"X"_4)/("n"_1 + "n"_2 + "n"_3 + "n"_4)`

= `(40 xx 50 + 35 xx 60 + 45 xx 55 + 42 xx 45)/(40 + 35 + 45 + 42)`

= `(2000 + 2100 + 2475 + 1890)/(162)`
= `(8465)/(162)`
= 52·25
Hence, the overall average maeks of perstudents is 52·25.