Basic Concept and Tricks on Mixture and alligation

By Anand Pandey|Updated : May 4th, 2019

Numerical ability section is considered to be one of the toughest subjects of RRB Exams. Mixture and Alligation is one of the toughest chapters in which candidates are confused. To make the chapter easy we are providing  Basic Concepts and Tricks on Mixture and Alligation which will surely make the chapter easy for all of you.

Alligation 

(i) To find the mean or average value of mixture when the prices of two or more ingredients which may be mixed together and the proportion in which they mixed are given.

(ii) To find the proportion in which the ingredients at given prices must be mixed to produce a mixture at a given price. 

Note:

(1) The word Alligation literally means linking. The rule takes its name from the lines or links used in working out questions on mixture.

(2) Alligation method is applied to the percentage value, ratio, rate, prices, speed etc and not for absolute values. That is, whenever per cent, per hour, per kg, per km etc, are being compared, we can use Alligation.

Rules of Alligation

if the gradients are mixed in a ratio, then

image001

We represent it as under:

image002

Then, (cheaper quantity) : (dearer quantity) = (d – m ) : (m – c)

 

Solved problems:

Ex1:  In what proportion must rice at Rs3.10 per kg be mixed with rice at Rs3.60 per kg, so that the mixture be worth Rs3.25 a kg?

Solution:

image003

By the alligation rule :image004

they must be mixed in the ratio 7 :3.

Milk and Water

Ex2: A mixture of certain quantity of milk with 16 liters of water is worth 90 P per liter. If pure milk be worth Rs1.08 per liter, how much milk is there in the mixture?

Solution:

The mean value is 90 P and price of water is 0 P.image006

By the Alligation Rule, milk and water are in the ratio of 5 :1.

quantity of milk in the mixture = 5 ×16 = 80 liters.

Ex3: 300 gm of sugar solution has 40% sugar in it. How much sugar should be added to make it 50% in the solution?

Solution:

The existing solution has 40% sugar, and sugar is to be mixed ; so the other solution has 100% sugar. So, by alligation method;

image007

the two mixture should be added in the ratio 5 :1

Therefore, required sugar =image008

Direct formula :

Quantity of sugar added =image009

In this case,

Ans =image010

 

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