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Class 8 Math (Assamese)

Course: Class 8 Math (Assamese)>Unit 1

Lesson 1: The role of 0 and 1

Inverse property of multiplication

Simple idea that multiplying by a number's multiplicative inverse gets you back to one. 5 × 1/5 = 1. Created by Sal Khan.

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• What would you do if you had to find a multiplicative inverse for a fraction?
• flip the fraction
multiplicative inverse of 2/5 = 5/2
• So the multiplicative inverse of 1 is 1/1?
• The multiplicative inverse of 1 is in fact 1/1 which is equal to 1. So 1 is its own multiplicative inverse.
• what about for 4/5 (4 over 5)? the additive inverse is 4/5 + (-4/5) = 0, but the multiplicative inverse!?
• It is the same concept as the video explains, except the video only demonstrates it using whole numbers. For example, with whole numbers, 15 is equivalent to 15/1 (15 over 1). To get that, you multiply by the multiplicative inverse of 15 - in this case, 1/15, by the original number, getting 1. Swapping the numerator and the denominator is the same concept. So for 4/5 (4 over 5), you would multiply it by 5/4 (5 over 4). It is the same steps, but your example is a fraction instead of a whole number. Let me know if I overcomplicated the answer to your question, and I will attempt to simplify it.
• What if we're dealing with negatives? Will this fraction thing still work?
• Yes it will still work. You just have to make sure that both numbers that you are multiplying are negative so that you end up with a positive one. (-72 x -1 / 72 = 1) That's a very important thing to keep in mind for higher level math. Good Question!
• I have a hard question in math it is 1c-7 then it says c-7 how is that possible if u don't know what c is?
• 1c means 1 times c. Therefore, you only have 1 of whatever c is, and you don't need to put the 1, because c=1c.
(1 vote)
• Why are there no practices for this?
• You can try practising fraction multiplication and division in Subject: Arithmetic .
• does ever problem with 1/8 = 1?
(1 vote)
• I don't know where you got the 1/8 from.
The inverse property of multiplication basically tells us:
any number * its reciprocal = 1

If you have a whole number like 5. Change it to its fraction 5/1. Its reciprocal = 1/5
The property tells us: 5/1 * 1/5 = 1

If you have a fraction like: 3/4. Its reciprocal = 4/3
The property tells us: 3/4 * 4/3 = 1

Hope this helps.
• I don't understand this concept one bit. My math teacher has tried to explain it but it's hopeless! Can someone please explain how to a problem such as a/13 =12?
• a/13=12 so, we already have the answer. All we need to do is multiply 13 times 12, because 13 under a is division. (You do the opposite thing) So, 13x12 is 156. a=156 Make sure you check your answer!
• It's called a reciprocal, right?
• That's right. The multiplicative inverse of a number is the reciprocal of that number.

a/b x b/a = 1 whatever a and b are.

a/b and b/a are reciprocals of one another.