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Course: 5th grade > Unit 6
Lesson 6: Multiplying fractions word problemsMultiply fractions: FAQ
Frequently asked questions about multiplying fractions.
How do we multiply fractions and whole numbers visually?
There are many different ways to multiply fractions visually. We can use area models, groups of objects, tape diagrams, or number lines. All of these methods help us to see how the multiplication works.
For example, we can use a number line to show how we multiply by drawing a number line from to and then splitting the number line into equal parts.
Next, we can find of on the number line by counting lengths of :
So, .
Try it yourself with these exercises:
What are the strategies we can use to multiply fractions by fractions?
Just like multiplying fractions and whole numbers, we can use different visuals to help us multiply fractions. Some popular strategies are using area models, tape diagrams, or number lines.
We can use an area model to multiply . First, we can create a striped rectangle by multiplying its
.
The striped rectangle would show of a unit wide and of a unit high. The amount overlapping would be our product. In this example, the product is .
Try it yourself with these exercises:
How do we multiply mixed numbers?
To multiply mixed numbers, we can convert them to improper fractions and then multiply the fractions as we normally would. For example, to multiply by , we first convert them to improper fractions: . Then, we multiply the numerators and denominators: .
Try it yourself with this exercise:
How do we find the area of rectangles with fraction side lengths?
To find the area of any rectangle, we can multiply the length times the width. If the rectangle has fractional side lengths, we multiply the two fractions together.
For example, to find the area of a rectangle with side lengths and , we multiply .
Try it yourself with this exercise:
Why do we need to learn how to multiply fractions?
Multiplying fractions is a key skill in math that you'll use throughout your academic career and in the real world. For example, if you need to scale a recipe up or down, you might need to multiply fractions in order to adjust the quantities of the ingredients.
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- After all the videos I still don't understand.Please make it more clear(5 votes)
- i will show you how to do it. example: 2/5 x 7/9. multiply the numerators and denominators, like this: 2x7=14, and 5x9=45. so the answer is 14/45(3 votes)
- What are "energy points" for?(2 votes)
- Energy points measure effort on Khan Academy. Learners earn more energy points by pushing the edge of their knowledge. They are not a measure of mastery or ability.
You can unlock new avatars with energy points.
Check out Learner Home > Click on your avatar
https://support.khanacademy.org/hc/en-us/articles/202487710-What-are-energy-points-badges-and-avatars(2 votes)
- Could you show me how it is done(2 votes)
- 1. Convert a mixed fraction to an improper fraction.
2. Multiply the numerator by each other, and this is the answer's numerator.
3. Multiply the denominator by each other, and this is the answer's denominator.
4. Simplify the fraction by dividing the result's numerator and denominator by their GCD.
For example, (7 / 2) * (15 / 7)
Numerator multiplied:
7 * 15 = 105
Denominator multiplied:
2 * 7 = 14
Our resultant fraction: 105 / 14
GCD of 105 and 14 is 7, so we divide numerator and denominator by 7.
(105 / 7) / (14 / 7)
= 15 / 2(2 votes)
- Thanks bro why did this help so much!(2 votes)
- Basically your multiplying the fractions instead of dividing?(2 votes)
- Yes, it wants you to divide, but it's multiplying, Kinda. It's confusing at the start.(1 vote)
- 7 divided by 21 equals 3?(1 vote)
- No. The order of division is important. While it is true that 21 divided by 7 is 3, 7 divided by 21 is the fraction 7/21, which reduces to 1/3.
Think about this: if 7 pizzas are equally divided among 21 people, each person would get less than a whole pizza because the number of pizzas (7) is less than the number of people sharing them (21). Clearly each person would not get 3 whole pizzas.(3 votes)
- I don't understand the videos and the question that says:
This is a square.
Thank you for that ground breaking information. I seem to have thought it was a circle. Thanks for clearing that up.(1 vote) - but how to do it with a mixed fraction(1 vote)
- There are 2 ways to do so.
1. Apply distributive law.
Note a mixed fraction (a b / c) is essentially (a + b / c). Hence,
(a b / c) * (d / e)
= (a + b / c) * (d / e)
= a * (d / e) + (b / c) * (d / e)
2. Convert mixed fraction to improper fraction.
It was covered before so I'm not going to explain it.
(a b / c)
= (a * c) / c + b / c
= (a * c + b) / c
(a b / c) * (d / e)
= (a * c + b) / c * (d / e)
https://www.khanacademy.org/math/cc-fourth-grade-math/imp-fractions-2/imp-mixed-numbers/v/changing-a-mixed-number-to-an-improper-fraction(1 vote)
- what are energy points for?(1 vote)