Question

The average earning of a person for the first four days of a week is $₹18$ and for the last four days is $₹22$. If he earns $₹20$ on the fourth day, what is average earning for the whole week?

• A. $₹16$
• B. $₹18$
• C. $₹20$
• D. $₹22$

Answer 1

The correct option is C $₹20$

The average earning of first four days $=(e_1+e_2+e_3+e_4)/4=18$
$=e_1+e_2+e_3+e_4=72........\left(1\right)$
The average earning of last four days $=(e_4+e_5+e_6+e_7)/4=22$
$=e_4+e_5+e_6+e_7=88$
We know that he earns $₹20$ on the fourth day.
Therefore,
$20+e_5+e_6+e_7=88$
$e_5+e_6+e_7=68........\left(2\right)$

Adding $\left(1\right)$ and $\left(2\right)$, we get,
The average earning $=(e_1+e_2+e_3+e_4+e_5$$+e_6+e_7)/7=140/7=₹20$