Questions on Average Money Expenditure:

Example-1

The average wages of a worker during a fortnight comprising 15 consecutive working days was Rs.90 per day. During the first 7 days, his average wages was Rs.87/day and the average wages during the last 7 days was Rs.92 /day. What was his wage on the 8th day?

Solution

The total wages earned during the 15 days that the worker worked : = 15 × 90 = Rs.1350.
The total wages earned during the first 7 days = 7×87 = Rs. 609.

The total wages earned during the last 7 days = 7×92 = Rs. 644.

Total wages earned during the 15 days = wages during first 7 days + wage on 8th day + wages during the last 7 days.

1350 = 609 + wage on 8th day + 644
wage on 8th day = 1350 − 609 − 644 = Rs. 97

Example-2

The average temperature on Wednesday, Thursday and Friday was 25circ. The average temperature on Thursday, Friday and Saturday was 24circ. If the temperature on Saturday was 27circ, what was the temperature on Wednesday?

Solution

Total temperature on Wednesday, Thursday and Friday was 25×3=75∘
Total temperature on Thursday, Friday and Saturday was 24×3=72∘
Hence, difference between the temperature on Wednesday and Saturday= 3∘
If Saturday temperature =27∘, then Wednesday’s temperature =27∘+3∘=30∘

Example-3

When a student weighing 45 kgs left a class, the average weight of the remaining 59 students increased by 200 g. What is the average weight of the remaining 59 students?

Solution

Let the average weight of the 59 students be A.

Therefore, the total weight of the 59 of them will be 59A

The questions states that when the weight of this student who left is added, the total weight of the class = 59 A + 45

When this student is also included, the average weight decreases by 0.2 kg.

Hence (59 A + 45)/60 = A − 0.2

⇒59 A + 45 = 60 A−12

⇒45 + 12=60A − 59A

⇒A=57

Example-4

Average cost of 5 apples and 4 mangoes is Rs. 36. The average cost of 7 apples and 8 mangoes is Rs. 48. Find the total cost of 24 apples and 24 mangoes.

Solution

Average cost of 5 apples and 4 mangoes = Rs. 36
Total cost = 36×9=324
Average cost of 7 apples and 8 mangoes = 48
Total cost = 48×15=720
Total cost of 12 apples and 12 mangoes = 324+720=1044
Therefore, cost of 24 apples and 24 mangoes = 1044 * 2 = 2088

Example 5: Nine persons went to a hotel. 8 persons spent Rs. 12 each on their meal and the ninth person spent Rs. 8 more than average expenditure of all nine. What was total money spent by them?

Solution:

Total money spent by 8 persons = 8 × 12 = Rs. 96

Let money spent by the 9th person = $x$
=> Total money spent by all the 9 persons $=96+x$
=> Average expenditure of all the 9 persons = $\frac{96+x}{9}$

Given, $x=\frac{96+x}{9}+8$
$\Rightarrow 9x=96+x+72$

$\Rightarrow 8x=168$

$\Rightarrow x=21$

$\Rightarrow 9x=96+x+72$

$\Rightarrow 8x=168$

$\Rightarrow x=21$

Total money spent by them $=96+x=96+21=117$