Multiplying Fractions
As we discussed in class, multiplying fractions is probably the easiest operation to perform with fractions. You don't have to find a common denominator to multiply fractions, you just have to know how to multiply. When you multiply fractions, you simply multiply the top numbers together and you multiply the bottom numbers together. For example:
3/4 * 5/6 = ?
Multiply the top numbers 3 * 5 = 15
Multiply the bottom numbers 4 * 6 = 24
So, 3/4 * 5/6 = 15/24 = 5/8
Now, there is a way to simplify before you multiply making your final answer easier to simplify or already simplified. This process is called cross simplifying and it only works during multiplication. Here is how it works. If there are numbers that are opposite of each other in the problem and they have something in common (something you can divide evenly into both numbers) then you can simplify those numbers. Here is the example again from above:
3/4 * 5/6 = ?
Since 3 and 6 are opposite each other in the problem and they have a 3 in common I can simplify those numbers. So the 3 on top becomes a 1 and the 6 on bottom becomes a 2. Here is the new problem.
1/4 * 5/2 = 5/8
Keep in mind that you get the same answer either way you do the problem, but when you are dealing with larger numbers it will make it easier on you if you can simplify before you multiply. Here are some steps to follow:
1. Change mixed numbers to improper fractions
2. Cross simplify if possible
3. Multiply the top numbers/multiply the bottom numbers
4. Simplify again if possible
Notice step one, if we are dealing with mixed numbers we must first convert them into improper fractions before we can work the problem. Unlike addition/subtraction you MUST change mixed numbers to improper fractions or you will get the wrong answer.
Here is an example of a mixed number problem:
3 3/5 * 1 5/9 = ?
18/5 * 14/9 =
2/5 * 14/1 = 28/5 = 5 3/5
If you run into problems remember you can post me a question and I will try respond.
3/4 * 5/6 = ?
Multiply the top numbers 3 * 5 = 15
Multiply the bottom numbers 4 * 6 = 24
So, 3/4 * 5/6 = 15/24 = 5/8
Now, there is a way to simplify before you multiply making your final answer easier to simplify or already simplified. This process is called cross simplifying and it only works during multiplication. Here is how it works. If there are numbers that are opposite of each other in the problem and they have something in common (something you can divide evenly into both numbers) then you can simplify those numbers. Here is the example again from above:
3/4 * 5/6 = ?
Since 3 and 6 are opposite each other in the problem and they have a 3 in common I can simplify those numbers. So the 3 on top becomes a 1 and the 6 on bottom becomes a 2. Here is the new problem.
1/4 * 5/2 = 5/8
Keep in mind that you get the same answer either way you do the problem, but when you are dealing with larger numbers it will make it easier on you if you can simplify before you multiply. Here are some steps to follow:
1. Change mixed numbers to improper fractions
2. Cross simplify if possible
3. Multiply the top numbers/multiply the bottom numbers
4. Simplify again if possible
Notice step one, if we are dealing with mixed numbers we must first convert them into improper fractions before we can work the problem. Unlike addition/subtraction you MUST change mixed numbers to improper fractions or you will get the wrong answer.
Here is an example of a mixed number problem:
3 3/5 * 1 5/9 = ?
18/5 * 14/9 =
2/5 * 14/1 = 28/5 = 5 3/5
If you run into problems remember you can post me a question and I will try respond.
posted by Joice Family at 11:58 AM
3 Comments:
Whats the best way to choose a number to divide with when I simplify
you better give me some extra credit for being the first person on your blog. i need to make up some extra points since we only got a completion grade on our last paper and i even made a good grade!!!!!
Natalie, sorry for the delay, I am so excited to know that someone actually got on line. I am sure your dad had nothing to do with it. When thinking about simplifying, you need to consider the divisibility rules that we learned in Chapter 4. For example, if we have to even number, we know that 2 will divide into them. If they aren't even and not easily recognizable then we might have to check our divisibility rules.
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