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### Course: MAP Recommended Practice>Unit 44

Lesson 13: Multiply & divide negative fractions

# Multiplying positive and negative fractions

See examples of multiplying and dividing fractions with negative numbers. Created by Sal Khan.

## Want to join the conversation?

• So if you add a negative to a negative, you get more negatives? Because I thought a negative plus a negative is a positive. I'm really confused
• Addition an subtraction can be seen as movement along the number line. Subtraction means move to the left of the line, while addition means move to the right. While the negative symbol on a number means move the opposite direction as you normally one.

Imagine this as a number line:
-5, -4, -3,-2,-1, 0 -1, 2, 3, 4, 5

if you have (-2) - 2 =?
You start at -2, move to the left two places, and your answer is -4.
If you have 5 - 7 =?
Then you start at 5, move to the left 7 places which places you at -2

If you're given 1 + (-2)=?
You start at 1, and with addition you usually move to the right, but it's a negative, or opposite to, so you move to the LEFT instead, ending at -1.
• At , why does Sal say that you can't simplify -21/20? Can't you simplify it to
-1 1/20? Or is it -21 over +20? :(
• The fraction is fully reduced as -21/20 (no common factors in numerator & denominator).
You can convert it to a mixed number, which you did correctly. It does become -1 1/20
• At , Sal. says that we cannot simplify 21/20 anymore. Can't we turn it into a mixed number, say 1 1/20?
• Good question! Yes, we can turn into a mixed number, but it is simplified as a fraction. numerator and denominator do not have any common factors other than 1.
• What would happen if you multiply a negative fraction and a positive fraction?
• If you multiply a negative by a positive you will always get a negative no matter if there is a decimal, fraction or whole number
• 5/9 X 3/15 . I don't understand the step where they both were divided by 15 in the above video.
• They were both divided by 15 because 5 times 3 is 15 and 9 times 15 is 135. Since both numbers had a GCF (Greatest Common Factor) of 15, Sal divided by 15 and received an answer of 1/9 because 15 divided by 15 is 1 and 135 divided by 15 is 9.

Unless you were looking for some other answer I suppose?
• whats the answer or work show for 7/2 x 1/6
• 7/2 x 1/6 = 7/12
You would multiply the two denominators and the two numerators to get 7/12.

If this helped I would really appreciate an upvote :)
• Can someone help I do not get this.
At all
• How would you draw a model for -7/10?
• at a negative times a negative= a positive so the answer would just be 1/9.
• Hi there!

I'm just a little confused. In the video "adding fractions with different signs" (not this video) we were taught to find the common denominator before addressing the numerator. However, here we aren't finding a common denominator first. What am I missing?

Thanks!