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chain rule[′chān ‚rül]
a method given in old arithmetic textbooks for converting the measures of one system into the measures of another system by means of a third system.
Suppose, for example, we want to know the number of vershki equal to 3 feet if 1 foot is equal to 12 inches and 28 inches are equal to 16 vershki. To apply the chain rule, we write the elements of the problem in the following form:
|x vershki||3 feet|
|1 foot||12 inches|
|28 inches||16 vershki|
The required number of vershki is obtained by dividing the product of the numbers in the right-hand column by the product of the known numbers in the left-hand column: