Week 7, May 18: Words for Adding & Subtracting Fractions

Common Denominator

A denominator that is the same in two or more fractions.

How can I subtract fractions when the denominators are the same?

If the denominators are the same, it is easy! The pieces are already the same size, so you can simply subtract the numerators. five ninths take away one ninth equals four ninths.

How can I add fractions when the denominators are the same?

It is easy! Just add the numerators. The pieces are already the same size, so you can simply count the number of pieces. three sevenths + two sevenths = five sevenths.

How to find the Least Common Multiple of 2 numbers.

List the multiples of both numbers. Circle the multiples that are the same. Use the smallest number that both lists have. Multiples of 6 are: 6, 12, 18, 24, 30, 36, 42, 48. Multiples of 8 are: 8, 16, 24, 32, 40, 48. They both have 24 and 48 but 24 is smaller. 24 is the Least Common Multiple of 6 and 8.

What is the sum of two fifteenths and three fifths?

The LCM of 15 and 5 is 15. Two fifteenths already has 15. Three fifths is the same as nine fifteenths. The sum eleven fifteenths.

What is one eighth plus one third?

The LCM of 8 and 3 is twenty four. One eighth equals three twenty fourths. One third equals eight twenty fourths. The sum is eleven twenty fourths.

Denominator.

The lower number in a fraction. The Denominator shows the SIZE of the pieces. Nine is a bigger number than four. But one ninth is a smaller piece than one fourth.

Multiples

The numbers you say when you skip count. Multiples of 2 are: 2, 4, 6, 8, 10, 12, 14, 16... Multiples of 25 are: 25, 50, 75, 100, 125, 150, 175, 200, 225...

Least

The smallest

Least Common Multiple (LCM)

The smallest multiple (other than zero) that two or more numbers have in common. The Least Common Multiple of 3 and 4 is 12.

Numerator.

The upper number in a fraction. The Numerator show HOW MANY pieces. One ninth has only one piece. Five ninths has five pieces. The pieces are all the same size,

How can I add fractions if the denominators are NOT the same?

To add fractions with "unlike denominators," you must change the fractions so that the Least Common Multiple is the denominator. Then you can add the numerators. The least common multiple of 2 and 3 is 6.

Unlike Denominator

Two fractions where denominators are not the same.