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### Course: 7th grade (Illustrative Mathematics)>Unit 5

Lesson 11: Lesson 11: Dividing rational numbers

# Dividing negative fractions

Created by Sal Khan.

## Want to join the conversation?

• why can you muliply a negative number by a negative number and make it a positive number?
• The two negative numbers cancel each other out, so if you have -1 * -2 you get 2, the same thing as 1 * 2. Hope this answers your question!
• HOw do I divide two negative fractions?
• Start by flipping the second fraction, so you are multiplying two negative fractions instead of dividing. Any time you multiply two negative numbers the negatives cancel each other out, so you can multiply the fractions as though they were both positive (the product of the numerators over the product of the denominators)
• With negative fractions, when someone writes this: -1/2, does that mean only the 1 is negative, or are both the 1 and the 2 negative?
• The expression -1/2 is going to be negative. It doesn't matter if you treat it like a fraction (minus one half) or like division (minus one divided by two). The 2 can also be negative instead (as in 1/-2) and it'll still be fundamentally the same. If you had -1/-2, that would actually be a positive number. If you had -(-1/2), that would also be a positive number. If you had -(-1/-2), that would actually be negative.
• What's another word for reciprocal?
• The best word to replace reciprocal is "complementary". But I think it is better to use reciprocal.
• What about 4/5 divided by 8/15 In simplest form?
• 4/5 divided by 8/15 is the same as 4/5*15/8 (not sure why). The numerators multiply 4*15 which is 60 and the denominator also does 5*8=40. This gives us 60/40 which is the same as 6/4 which is the same as 3/2 or 1.5.
• Could we have a round of applause for Sal he helps many people to get better at math and more!
• couldn't Sal cross multiply
• Yep, he could but not necessary since its just for beginners to learn the concept