Sal shows us how to change mixed numbers into improper fractions, divide, and then change the answer back to a mixed number. Created by Sal Khan and Monterey Institute for Technology and Education.
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- What is the reciprocal?(82 votes)
- A reciprocal of a fraction is when you flip the numerator and denominator. Such as the reciprocal of 6/10 is 10/6.(6 votes)
- How do I do an equation like: 5/-8 ÷ 1 3/7, with a negative denominator? Please answer this ASAP, I really need help with this.(4 votes)
- You can always do the signs apart from the numbers. In multiplying and dividing, you count number of negative signs. With 0, 2, 4, 6, ... answer is positive, if 1, 3, 5, 7, ... answer is negative. In your example, you only have 1 negative, so answer is negative then do (5/8)/(1 3/7).(5 votes)
- Can you show me how to do this problem? 4 1/2 divided by 3? I don't get it.(3 votes)
- wait, why is two fourths the same as eight fourths?(2 votes)
- but how do I divide negative numbers?(3 votes)
- Note: These rules for dividing also apply for multiplication
A negative divided by a negative is a positive
A negative divided by a positive is a negative
A positive divided by a positive is a positive(4 votes)
- A seven and half(7 1/2) tub has only one fifth(1/5) of water.
how many gallons of water is in the tub?
Can anybody solve this problem step by step?(4 votes)
- The heck is that black magic at the start(3 votes)
Divide. Simplify the answer and write as a mixed number. And we have 2 and 1/4 divided by 1 and 3/4. So the first thing we want to do since both of these are mixed numbers is to convert them both into improper fractions. So let's start with 2 and 1/4. So we're still going to have 4 in the denominator, but instead of 2 and 1/4, remember, 2 is the same thing as 8/4. So we have 8/4, and then we have another 1/4. That gives us 9/4. Or another way to come up with this 9, you take 4 times 2, which is 8, plus 1. That gives you 9. And then the 1 and 3/4, same process. You're going to have 4 in the denominator, and then the numerator is going to be 4 times 1, which is 4, plus 3, which is 7. So this is the exact same problem here. 2 and 1/4 divided by 1 and 3/4 is the same thing as 9/4 divided by 7/4. And we saw in several videos already that dividing by a fraction is the same thing as multiplying by its reciprocal. So this is equivalent to-- so these are all equivalent. This is equivalent to 9/4 times the reciprocal of this. We're changing the division operation to a multiplication, and we're taking the reciprocal of the 7/4. For the reciprocal of 7/4, you swap the numerator and denominator, or the top number and the bottom number, and you get 4/7. Now, we could just multiply these. We could just say this is 9 times 4, which would be 36, over 4 times 7, which is 28, and then try to put it in lowest terms, or we could do it right now because it would be simpler. We have a 4 in the numerator. We have a 4 in the denominator, that'll eventually be in the denominator, so let's divide our eventual numerators and our eventual denominators both by 4. So you divide this 4 by 4, you get 1. This 4 by 4, you get 1. So now when you multiply it, you get 9 times 1, which is 9, over 1 times 7, which is 7. So we have our answer, but right now, it's an improper fraction. They want us to write it as a mixed number. And to figure it out as a mixed number, we can do it in our heads now. I think we've seen this enough times. We say how many times does 7 go into 9? Well, it goes into it exactly one time, but when you take 7 into 9 one time, what do you have left over? Well, you're going to have 2 left over, right? 7 times 1 is 7, and you're going to have 2 left over. You need 2 more to get to 9. So you're going to have 2 left over, so this is 1 and 2/7. And we're done!