This section is from the book "The American House Carpenter", by R. G. Hatfield. Also available from Amazon: The American House Carpenter.

The process resorted to in the last article to equalize the denominators, is not always successful. What is needed for a common denominator is to find the smallest number which shall be divisible by each of the given denominators. Before seeking this number, let each given fraction be reduced to its lowest terms, by dividing each factor by a common number. For example: 5/15 may, by dividing by 5, be reduced to 1/3, which is its equivalent. So, also, 21/28, by dividing by 7, is reduced to 3/4, its lowest terms.

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