Aptitude - Average - Discussion
Discussion Forum : Average - General Questions (Q.No. 9)
9.
A car owner buys petrol at Rs.7.50, Rs. 8 and Rs. 8.50 per litre for three successive years. What approximately is the average cost per litre of petrol if he spends Rs. 4000 each year?
Answer: Option
Explanation:
| Total quantity of petrol consumed in 3 years |
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Total amount spent = Rs. (3 x 4000) = Rs. 12000.
 Average cost = Rs. |
 |
12000 x 51 |  |
= Rs. | 6120 | = Rs. 7.98 |
| 76700 | 767 |
Discussion:
92 comments Page 5 of 10.
Santhosh Sandy said:
9 years ago
In the solution how they got 4000(2/15+1/8+2/17) = (76700/51) ?
I'm bit confused :-(.
I'm bit confused :-(.
Ashwini madne said:
9 years ago
@Santhosh Sandy.
= 4000/7.50 + 4000/8 + 4000/8.50.
= 4000(1/7.50 + 1/8 + 1/8.50) ...... 1/7.50.
It can be written as 100/750 which is equal to 2/15 same as 1/8.50 can be written as 100/850 which is equal to 2/17.
= 4000(2/15 + 1/8 + 2/17).
= 4000[{(2 * 8) + (15 * 1)/15 * 8} + 2/17].
= 4000[{31/120 + 2/17}].
= 4000[767/2040].
= 76700/51.
= 4000/7.50 + 4000/8 + 4000/8.50.
= 4000(1/7.50 + 1/8 + 1/8.50) ...... 1/7.50.
It can be written as 100/750 which is equal to 2/15 same as 1/8.50 can be written as 100/850 which is equal to 2/17.
= 4000(2/15 + 1/8 + 2/17).
= 4000[{(2 * 8) + (15 * 1)/15 * 8} + 2/17].
= 4000[{31/120 + 2/17}].
= 4000[767/2040].
= 76700/51.
(1)
Varma said:
9 years ago
Why take 7.50 + 8 + 8.50 / 3 = 8?
Swaroopa said:
9 years ago
Thank you all for the explanation.
Sandeep said:
9 years ago
Only for this question based upon the options.
Think generally for three years amount is same but the purchasing of petrol is different.
The average is approximately 8 rupees. But in the first year we are purchasing the oil with low price then we get more petrol with the same amount than the other years.
By observing this we get something more in the denominator (petrol quantity) so absolutely numerator value decreases very less than the average (rs. 8).
By seeing options we can say 7.9 is the answer.
Think generally for three years amount is same but the purchasing of petrol is different.
The average is approximately 8 rupees. But in the first year we are purchasing the oil with low price then we get more petrol with the same amount than the other years.
By observing this we get something more in the denominator (petrol quantity) so absolutely numerator value decreases very less than the average (rs. 8).
By seeing options we can say 7.9 is the answer.
Akashay said:
9 years ago
Is there any shortcut to solve this problem?
Venkat said:
9 years ago
Please solve this equation 4000(2/15 + 1/8 + 2/17) = ?
(1)
Arvind Sahu said:
9 years ago
As we know,
Average = (tatal cost) / (total quantity).
So according to this question, he is spending 4000/- per yr for 3 corresponding yr.
So total cost become:-
Total cost=4000*3=> 12000/-
And to find total quantity we have to find seperatly first and then add them-
1st yr (4000/7.5) = 533.3,
2nd yr (4000/8) = 500,
3rd yr (4000/8.50) = 470.5.
Total quantity = 533.3 + 500 + 470.5 = 1503.8.
Now we can easily divide and find the average like:-
Required Average = 12000/1503.8
= 7.98 answer.
Average = (tatal cost) / (total quantity).
So according to this question, he is spending 4000/- per yr for 3 corresponding yr.
So total cost become:-
Total cost=4000*3=> 12000/-
And to find total quantity we have to find seperatly first and then add them-
1st yr (4000/7.5) = 533.3,
2nd yr (4000/8) = 500,
3rd yr (4000/8.50) = 470.5.
Total quantity = 533.3 + 500 + 470.5 = 1503.8.
Now we can easily divide and find the average like:-
Required Average = 12000/1503.8
= 7.98 answer.
(2)
D Trimurtulu said:
9 years ago
I did not understand this way. Any other way to simplify this problem? Please explain me.
Jeevan said:
8 years ago
Nice, thanks for the explanation @Arvind.
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