# The average of three numbers be 21. If two of the numbers are 4 and 12, what is the remaining number?

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The average of three numbers be 21. If two of the numbers are 4 and 12, what is the remaining number?
1. 20
2. 30
3. 47
4. 52

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Correct Answer - Option 3 : 47

Concept:

$\rm Mean\ of\ 'n'\ observations=\dfrac{Sum\ of\ observations}{n}$.

Calculation:

Let's say that the third number is x.

So, Numbers are 4, 12 and x

Here n = 3

As we know, $\rm Mean\ of\ 'n'\ observations=\dfrac{Sum\ of\ observations}{n}$

∴ $\rm 21=\dfrac{4+12+\rm x}{3}$

⇒ x + 16 = 63

⇒ x = 47.