Question

Of the four numbers whose average is $60$, the first is ${\frac{1}{4}}^{th}$ of the sum of the last three. The first number is

• A. $15$
• B. $45$
• C. $48$
• D. $60.25$

Answer 1

The correct option is C $48$

Let the numbers be $a,b,c,d$.

Then, $\frac{a+b+c+d}{4}=60$

$\Rightarrow a+b+c+d-=240$ .......(1) and

$a=\frac{1}{4}(b+c+d)$

$\Rightarrow b+c+d=4a$ .......(2)
$\therefore$ equation (1) and (2), we have
$a+4a=240$

$\Rightarrow 5a=240$

$\Rightarrow a=48$