In the example given in the last article it will be observed that the product of the denominators of the two given fractions equals the area of the whole figure (A B CD), while the product of the numerators equals the area of the rectangle (E F A G), the sides of which are equal respectively to the given fractions. From this we obtain for the product of fractions this -
RULE. - Multiply together the denominators for the new denominator, and the numerators for a new numerator.
For example: what is the product of 13/21 and 7/20? Here we have 20x21=420 for the new denominator, and
7 x 13 = 91 for the new numerator; therefore the product of -
or, of a rectangular area divided one way into 20 parts and the other way into 21 parts, thus containing 420 rectangles, the product of the two fractions 13/21 and 7/20 is equal to 91 of these rectangles, or91/420of the whole.