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hi Bunuel, i solved this question by below method, could you please verify if it's alright? please provide an easy solution for this question. And can allegation be used here? if so, how?

i went by options,
a) 4:1 if the total quantity is 10, milk is 8 and water is 2, if the cp of milk is 10/liter, then milk cp will be 8 and total price will be 100 but 20% profit leads to 96, so this ain't it.
b) 5:1 if the total quantity is 12, milk is 10 and water is 2, if the cp of the milk is 10/liter, then milk cp will be 100 and total price will be 120, which is in fact 20% of 100.
so i picked it. If the correct answer choice was incase in the bottom, i would've lost a track of time before getting to it by trail and error, so i need an easy and quick method here.

Thanks much in advance, I also wanna add that your real quick replies are actually so helpful and I appreciate you a lot for all the things you do for this community. May your coffee always be the perfect temperature.

thanks much,
Swetha

Bunuel
A milk vendor sells milk at Cost Price but still gains 20%. Find the ratio of milk and water in every gallon that he sells.

A. 4:1
B. 5:1
C. 5:2
D. 6:1
E. None of these


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SwethaReddyL
hi Bunuel, i solved this question by below method, could you please verify if it's alright? please provide an easy solution for this question. And can allegation be used here? if so, how?

i went by options,
a) 4:1 if the total quantity is 10, milk is 8 and water is 2, if the cp of milk is 10/liter, then milk cp will be 8 and total price will be 100 but 20% profit leads to 96, so this ain't it.
b) 5:1 if the total quantity is 12, milk is 10 and water is 2, if the cp of the milk is 10/liter, then milk cp will be 100 and total price will be 120, which is in fact 20% of 100.
so i picked it. If the correct answer choice was incase in the bottom, i would've lost a track of time before getting to it by trail and error, so i need an easy and quick method here.

Thanks much in advance, I also wanna add that your real quick replies are actually so helpful and I appreciate you a lot for all the things you do for this community. May your coffee always be the perfect temperature.

thanks much,
Swetha


Your option-based method is valid, but the calculations for option A need to be stated more clearly.

For option A, milk : water = 4 : 1. Assume there are 10 liters of mixture, containing 8 liters of milk and 2 liters of water. If milk costs $10 per liter:

Cost = 8 * $10 = $80
Selling price = 10 * $10 = $100
Profit = $20

The profit percentage is calculated on the cost:

20/80 * 100 = 25%

Therefore, option A does not give a 20% profit.

For option B, milk : water = 5 : 1. Assume there are 12 liters of mixture, containing 10 liters of milk and 2 liters of water:

Cost = 10 * $10 = $100
Selling price = 12 * $10 = $120
Profit = $20

Thus, the profit is 20% of the cost, so option B is correct.
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Let m = quantity of milk.
Let w = quantity of water.
Since he sells the mixture at the cost of pure milk:
CP = m
SP = m + w
He gains 20%, so:
SP/CP = 120/100 = 12/10
Therefore,
(m + w)/m = 12/10
10m + 10w = 12m
10w = 2m
m/w = 5/1
Therefore,
Milk : Water = 5 : 1
Answer: B) 5:1
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