ABC26GN1574 · Average

Subject: General Aptitude · Chapter: Average · Exam: 2009 · Marks: · Difficulty:

The mean of 5 observations is 60, the mean of 10 observations is 30 and the mean of 15 observations is 20 . The mean of all the 30 observations is

(a)20

(b)25

(c)30

(d)40

Answer

Answer (as printed): C

Explanation

$$\begin{aligned} \text { Required mean } & =\left(\frac{60 \times 5+30 \times 10+20 \times 15}{5+10+15}\right) \\ & =\left(\frac{300+300+300}{30}\right)=\frac{900}{30}=30 . \end{aligned}$$

Explanation as extracted from the printed page; notation may be imperfect.

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