Alligation
Encyclopedia
Alligation is an old and practical method of solving arithmetic
problems related to mixtures of ingredients. There are two types of alligation: alligation medial, used to find the quantity of a mixture given the quantities of its ingredients, and alligation alternate, used to find the amount of each ingredient needed to make a mixture of a given quantity. Alligation medial is merely a matter of finding a weighted mean
. Alligation alternate is more complicated and involves organizing the ingredients into high and low pairs which are then traded off.
, 1/4 Sprite
, and 1/4 orange soda. The Coke has 120 grams of sugar per liter, the Sprite has 100 grams of sugar per liter, and the orange soda has 150 grams of sugar per liter. How much sugar does the drink have? This is an example of alligation medial because you want to find the amount of sugar in the mixture given the amounts of sugar in its ingredients. The solution is just to find the weighted average by composition:
grams per liter
to yield 16/5, and the amounts of the two ingredients are
ounces whole milk and 
ounces low fat milk.
Arithmetic
Arithmetic or arithmetics is the oldest and most elementary branch of mathematics, used by almost everyone, for tasks ranging from simple day-to-day counting to advanced science and business calculations. It involves the study of quantity, especially as the result of combining numbers...
problems related to mixtures of ingredients. There are two types of alligation: alligation medial, used to find the quantity of a mixture given the quantities of its ingredients, and alligation alternate, used to find the amount of each ingredient needed to make a mixture of a given quantity. Alligation medial is merely a matter of finding a weighted mean
Weighted mean
The weighted mean is similar to an arithmetic mean , where instead of each of the data points contributing equally to the final average, some data points contribute more than others...
. Alligation alternate is more complicated and involves organizing the ingredients into high and low pairs which are then traded off.
Alligation medial
Suppose you make a cocktail drink combination out of 1/2 CokeCoca-Cola
Coca-Cola is a carbonated soft drink sold in stores, restaurants, and vending machines in more than 200 countries. It is produced by The Coca-Cola Company of Atlanta, Georgia, and is often referred to simply as Coke...
, 1/4 Sprite
Sprite (soft drink)
Sprite is a transparent, lemon-lime flavored , caffeine free soft drink, produced by the Coca-Cola Company. It was introduced in the United States in 1961. This was Coke's response to the popularity of 7 Up, which had begun as "Bib-Label Lithiated Lemon-Lime Soda" in 1929...
, and 1/4 orange soda. The Coke has 120 grams of sugar per liter, the Sprite has 100 grams of sugar per liter, and the orange soda has 150 grams of sugar per liter. How much sugar does the drink have? This is an example of alligation medial because you want to find the amount of sugar in the mixture given the amounts of sugar in its ingredients. The solution is just to find the weighted average by composition:
grams per literAlligation alternate
Suppose you like 1% milk, but you have only 3% whole milk and ½% low fat milk. How much of each should you mix together to make an 8 ounce cup of 1% milk? This is an example of alligation alternate because you want to find the amount of two ingredients to mix together to form a mixture with a given amount of fat. Since there are only two ingredients, there is only one possible way to form a pair. The difference of 3% from the desired 1%, 2%, is assigned to the low fat milk, and the difference of ½% from the desired 1%, ½%, is assigned alternately to the whole milk. The total amount, 8 ounces, is then divided by the sum to yield 16/5, and the amounts of the two ingredients are ounces whole milk and ounces low fat milk.