Alligation or Mixture - General Aptitude

Q1:

A dishonest milkman professes to sell his milk at cost price but he mixes it with water and thereby gains 25%. The percentage of water in the mixture is:

A 4%

B
 
6%

C 20%

D 25%

ANS:C - 20%

Let C.P. of 1 litre milk be Re. 1 Then, S.P. of 1 litre of mixture = Re. 1, Gain = 25%.

C.P. of 1 litre mixture = Re. 100 x 1 = 4
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By the rule of alligation, we have:
C.P. of 1 litre of milk C.P. of 1 litre of water
Re. 1 Mean Price
Re. 4
5
0
4
5
1
5
Ratio of milk to water = 4 : 1 = 4 : 1.
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Hence, percentage of water in the mixture = 1 x 100 % = 20%.
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