Question

The average of 5 observations is 12. If the average of the first 3 observations is 10, then find the average of the other two.

• A. 10
• B. 12
• C. 15
• D. 12.5

Answer 1

The correct option is C 15

Let us suppose that the value of 5 observations is a , b, c, d, e. Now average of 5 observations can be represented as $\frac{a+b+c+d+e}{5}=12$ .
Hence, a+b+c+d+e = 60.....(i) .
It is also given that the average of the first three observations is 10
$\Rightarrow$ $\frac{a+b+c}{3}=10$. $\Rightarrow$ a+b+c =30...........(ii)
From (i) and (ii) we get
d + e = 30.
Hence, the average of the other two observations i.e. 'd' and 'e' is
$\frac{d+e}{2}=15$