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All questions of Mixtures & Alligations for UPSC CSE Exam

8 litres are drawn from a cask full of wine and is then filled with water. This operation is performed three more times. The ratio of the quantity of wine now left in cask to that of the water is 16:65. How much wine did the cask originally hold?
  • a)
    30 litres
  • b)
    26 litres
  • c)
    24 litres
  • d)
    32 litres
Correct answer is option 'C'. Can you explain this answer?

Arya Roy answered
8 litres are drawn from a cask full of wine and is then filled with water.
This operation is performed three more times.
The ratio of the quantity of wine now left in cask to that of the water is 16 ∶ 65
Calculations:
Let the quantity of the wine in the cask originally be x litres.
After first operation, wine left in the cask = (x - 8) litres So, the ratio of the quantity of wine now left in cask to that of filled cask = 
This operation is performed three more times. Then, Wine : Water = 16 : 65 or wine : water = 16 : (16 + 65) = 81
Correct answer is 24.

A mixture of 100 litres of spirit and alcohol contains 25% alcohol. How much more alcohol should be added to the mixture to increase the percentage of alcohol to 30% in the new mixture?
  • a)
    3.33 litres
  • b)
    7.14 litres
  • c)
    5 litres
  • d)
    4 litres
Correct answer is option 'B'. Can you explain this answer?

Kavya Sharma answered
Alcohol content in the alcohol to be added = 100%
Therefore, the allegation diagram for this problem can be drawn as:
Therefore, ratio of the mixture to alcohol = 70/5 = 14/1
So, alcohol to be added = 100/14
Hence, the answer is "7.14 litres".
Choice B is the correct answer.

How many kilograms of sugar costing Rs. 9 per kg must be mixed with 27 kg of sugar costing Rs. 7 per Kg so that there may be a gain of 10 % by selling the mixture at Rs. 9.24 per Kg ?

  • a)
    60 Kg
  • b)
    63 kg
  • c)
    58 Kg
  • d)
    56 Kg
Correct answer is option 'B'. Can you explain this answer?

C.P. of 1 kg sugar of 1st kind      C.P. of 1 kg sugar of 2nd kind

Therefore, Ratio of quantities of 1st and 2nd kind = 14 : 6 = 7 : 3. 

Let x kg of sugar of 1st kind be mixed with 27 kg of 2nd kind. 

Then, 7 : 3 = x : 27 or x = (7 x 27 / 3) = 63 kg.

Tea worth Rs. 126 per kg and Rs. 135 per kg are mixed with a third variety of tea in the ratio 1 : 1 : 2. If the mixture is worth Rs. 153 per kg, what is the price of the third variety per kg ?
  • a)
    Rs.182.50
  • b)
    Rs.170.5
  • c)
    Rs.175.50
  • d)
    Rs.180
Correct answer is option 'C'. Can you explain this answer?

Manoj Ghosh answered
Since first and second varieties are mixed in equal proportions.

So, their average price = Rs.
126 + 135/2
= Rs. 130.50
So, the mixture is formed by mixing two varieties, one at Rs. 130.50 per kg and the other at say, Rs. x per kg in the ratio 2 : 2, i.e., 1 : 1. We have to find x.

By the rule of alligation, we have:

 x - 153 = 22.50
 x = 175.50

A milk vendor has 2 cans of milk. The first contains 25% water and the rest milk. The second contains 50% water. How much milk should he mix from each of the containers so as to get 12 litres of milk such that the ratio of water to milk is 3 : 5?

  • a)
    5 litres, 7 litres
  • b)
    7litres, 4 litres
  • c)
    6litres, 6 litres
  • d)
    4litres, 8 litres
Correct answer is option 'C'. Can you explain this answer?

Ishani Rane answered
Let x and (12-x) litres of milk be mixed from the first and second container respectively
Amount of milk in x litres of the the first container = .75x
Amount of water in x litres of the the first container = .25x
Amount of milk in (12-x) litres of the the second container = .5(12-x)
Amount of water in (12-x) litres of the the second container = .5(12-x)
Ratio of water to milk = [.25x + .5(12-x)] : [.75x + .5(12-x)] = 3 : 5
⇒ (.25x+6-5x)/(.75x+6-.5x) =3/5
⇒(6−.25x)/(.25x+6) =3/5
⇒30−1.25x=.75x+18
⇒2x=12
⇒x=6
Since x = 6, 12-x = 12-6 = 6
Hence 6 and 6 litres of milk should mixed from the first and second container respectively

Two vessels A and B contain spirit and water in the ratio 5 : 2 and 7 : 6 respectively. Find the ratio in which these mixture be mixed to obtain a new mixture in vessel C containing spirit and water in the ration 8 : 5 ?
  • a)
    3: 4
  • b)
    4 : 3
  • c)
    9 : 7
  • d)
    7 : 9
Correct answer is option 'D'. Can you explain this answer?

Manoj Ghosh answered
Spirit in 1 litre mix of A = 5/7 litre.
Spirit in 1 litre mix of B = 7/13 litre.
Spirit in 1 litre mix of C = 8/13 litre. 
By rule of alligation we have required ratio X:Y

   X         :       Y

 5/7              7/13

 

       \          /
          (8/13)

       /          \


(1/13)     :     (9/91)

  7                      9

Therefore required ratio = 1/13 : 9/91 

= 7:9

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