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### Course: MAP Recommended Practice>Unit 36

Lesson 5: Adding & subtracting negative fractions

Add and subtract negative fractions with unlike denominators. Created by Sal Khan.

## Want to join the conversation?

• From to , Sal says "then we add 3/4 to -10/6." But why add? Should the distributive property apply and we multiply? Vote up if this is a question you have too, please.
• The distributive property only applies if you're multiplying. Here, you're just adding the three fractions together. It looks confusing because Sal separated two of the fractions and added them together and then he added the third one to those two, but what you're doing to the fractions didn't change -- it's still just three fractions being added.
• but the negative + negative = positive .. why you put it as -29 ?
• Negative + negative = a smaller (bigger-looking) negative number. I think you are confusing this with multiplication, where negative x negative = positive. A way to remember is to look at a number line and use easy numbers (1, -1) to figure out the negatives and positives.
• Is the numerator the only number in the fraction to be negative?
• If one part of a fraction is negative, it means that the whole fraction is negative. It doesn't matter if you put the negative sign in front of the numerator or in front of the denominator, both of them will cause the fraction to be negative. However, you won't see a fraction with both a negative numerator and a negative denominator, because the negatives would cancel each other out and the entire fraction would become positive.
• Can the denominator of a fraction be negative, or is that a nono?
• The denominator of a fraction can be negative, but it can not be zero.
• This makes honestly no sense to me... HOW DO YOU DO THIS?
• I still don't get why you change it into a positive.
• Unfortunately this is wrong, -2+(-3) would equal -5.
Two negative numbers result in a positive movement only when one is subtracted from another eg: -2-(-3) = 1
So you start with -2 and to add -3 you would go three steps <--- to subtract -3 you must go three steps --->
The best way to visualise this is to look at a number line. Watch Sal's videos on adding and subtracting negative numbers again and try drawing your own number lines. Best of luck!
• At -, why would you add -3/4 to -7-3/6? I don't get that.
• taking away a positive number from a negative is the same as adding its positive. if you had a problem like -3-4, that would be the same thing as -3 plus -4. just like in the fractions,
-3/4-(-7)-3/6 is the same thing as -3/4 plus -7-3/6.
• 7 1/2 - 2 7/10 = ? I keep getting 5 4/10 is this correct?
• No, but close. 7 (1/2) - 2 (7/10) can be converted into improper fractions:
(75/10) - (27/10) = ?
Subtracting gives 48/10 or 4 (8/10) = 4 (4/5)