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The Question & Answer (Q&A) Knowledge Managenet

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Table of Contents

- When adding and subtracting fractions the denominators must be?
- When adding and subtracting fractions all answer must be expressed in the?
- Do you add denominators when adding fractions?
- How do you add fractions with the same denominators?
- When subtracting fractions with different denominators What is the first step?
- What is the trick to subtracting fractions?
- How do you find the lowest common multiple?
- What are the first 3 multiples of 5?
- What is the least common multiple of 3 9 and 10?
- What is the LCM of 3 and 9 and 12?

1. How do we add or subtract fractions? The names of what we are adding or subtracting — the denominators — must be the same. Add or subtract only the numerators, and keep that same denominator.

To add or subtract fractions, they must have a common denominator. To add or subtract fractions, add or subtract the numerators and place the result over the common denominator.

If the denominators are not the same, then you have to use equivalent fractions which do have a common denominator . To add fractions with unlike denominators, rename the fractions with a common denominator. Then add and simplify.

Instructions for adding fractions with the same denominator

- Build each fraction (if needed) so that both denominators are equal.
- Add the numerators of the fractions.
- The new denominator will be the denominator of the built-up fractions.
- Reduce or simplify your answer, if needed. Factor the numerator.

How to subtract fractions with different denominators

- Step 1: Find the least common denominator. Find the least common denominator (LCD) of the fractions.
- Step 2: Find the equivalent fraction. Find the equivalent fraction of each fraction, so that they all have the LCD as the denominator.
- Step 3: Subtract the new numerators.
- Step 4: Simplify if necessary.

Subtract fractions with the easy method Here’s the easy way to subtract fractions that have different denominators: Cross-multiply the two fractions and subtract the second number from the first to get the numerator of the answer. After you cross-multiply, be sure to subtract in the correct order.

One way to find the least common multiple of two numbers is to first list the prime factors of each number. Then multiply each factor the greatest number of times it occurs in either number. If the same factor occurs more than once in both numbers, you multiply the factor the greatest number of times it occurs.

The first few multiples of 5 are 5, 10, 15, 20, 25, 30, and so on. We get successive multiples of 5 by skip counting. If we skip count 108 times by 5, we will get the 108 th multiple of 5, i.e., 108 × 5 = 540. We can also find the multiples of 5 using the multiplication table of 5.

Answer: LCM of 3, 10, 9 is 90.

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