Question

In a class there are 20 juniors, 15 seniors and 5 graduate students. If the junior averaged 65 in the midterm exam, the senior averaged 70 and the graduate students averaged 91, then what is the mean of the centre class approximately?

(a) 71

(b) 74

(c) 70

(d) 72

The question was posed to me in semester exam.

I'm obligated to ask this question of Statistics topic in chapter Statistics of Mathematics – Class 11

Answer 1

Correct option is (c) 70

To elaborate: Combined mean = (Σ xini)/(Σ ni) = (20 × 65 + 15 × 70 + 5 × 91)/(20 + 15 + 5) = 70.