Читать книгу Algebra I All-in-One For Dummies - Mary Jane Sterling, Mary Sterling Jane - Страница 85

You can add fractions together or subtract one from another if they have a common denominator. After you find the common denominator and change the fractions to their equivalents, you can add the numerators together or subtract them (keeping the denominators the same).

Adding and subtracting fractions takes a little special care. You can add quarts and gallons if you change them to the same unit. It’s the same with fractions. You can add thirds and sixths if you find the common denominator first.

To add or subtract fractions:

1 Convert the fractions so that they have the same value in the denominators.Find out how to do this in the section, “Finding common denominators.”

2 Add or subtract the numerators.Leave the denominators alone.

3 Reduce the answer, if needed.

Q. In her will, Jane gave of her money to the Humane Society and of her money to other charities. How much was left for her children’s inheritance?

A. The fractions and aren’t compatible because the denominators don’t have any factors in common. The fraction has the larger denominator and can be written as or or , and so on. You can stop at because 3 divides 21 evenly: and . Add the numerators to get the total designation to charity in Jane’s will: . Subtract that total from the whole of Jane’s proceeds to find what portion is allotted to her children: . Jane’s children will be awarded of her estate.

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A. First find the common denominator, 24, and then complete the addition:

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A. You need a common denominator of 30:

The whole number parts are separated from the fractional parts to keep the numbers in the computations smaller. Be sure to apply the subtraction to both the whole number and fraction when needed.

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A. In this problem, you see another option: you can change both mixed numbers to improper fractions. The common denominator is 56:

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