How to subtract mixed numbers that have unlike denominators | Fractions | Pre-Algebra | Khan Academy

2m read

·Nov 10, 2024

Let's try to evaluate 7 and 6 9ths - 3 and 25ths.

So, like always, I like to separate out the whole number parts from the fractional parts. This is the same thing as 7 + 6/9 - 3 - 25/100. The reason why I'm saying -3 and -25/100 is this is the same thing as -3 + 25/100.

So, you distribute the negative sign: you're subtracting a 3 and then you're subtracting the 25/100. Now we can worry about the whole number parts: 7 - 3. Well, 7 minus 3 is going to give us 4. So that's going to give us 4.

Then we're going to have 6/9 - 25/100. Let me think about what 6/9 - 25/100 is. We're going to have to find a common denominator. The least common multiple of 9 and 100 is going to be 900.

Now, they have no common factors, so it's going to be over 900. To go from 9 to 900, I have to multiply by 100. So, I'm going to have to multiply the numerator by 100: 6 * 100 is 600.

To go from 100 to 900, I had to multiply by 9, so I have to multiply the numerator by 9 if I don't want to change the value: 25 * 9 is 225.

So, 600/900 - 225/900 is going to be something over 900. 600 minus 225 is 375. So this is, if I subtract these two fractions right over here, I get 375/900.

So it's 4 + 375/900. If we wanted to write it as a mixed number, this is equal to 4 and 375/900, but we're not done yet.

We can simplify this further: 375 and 900 have common factors. They are both divisible by 75. So, we can say that this is actually...

If we divide the numerator by 75 and the denominator by 75, we end up with 4 and 375/75 is 5, and 900/75 is 12.

So we have 4 and 5/12. Actually, we're done. These two can't be simplified anymore: 4 and 5/12.

Compare rational numbers using a number line

Safari Live - Day 329 | National Geographic

View All

Is Something in Space Talking to Us? | StarTalk

So there are some signals that exist in the record books. Right? And to some, that means the aliens have already tried to contact us. In 1977, the Ohio State University had a big radio telescope. It’s been turned, I think, into a golf course now. But one …

Shoguns, samurai and the Japanese Middle Ages | World History | Khan Academy

As we get into the late Heian period, you start to have the emergence of an increasingly powerful warrior class. All of that comes to a head in the year 1185 when the Heian period ends, and a general by the name of Minamoto Yoritomo comes to power. What’s…

r-selected and K-selected population growth strategies | High school biology | Khan Academy

What we’re going to do in this video is talk about different population growth strategies for different species and think about if we can come up with a broad categorization or if there’s a broad categorization already out there for us. We see that there…

Portraits of Afghanistan Before the Fall | Podcast | Overheard at National Geographic

[Music] 20 years after the United States went into Afghanistan to pursue Osama bin Laden, U.S. forces have finally withdrawn and the hard-line Islamist Taliban regime has once again seized control of the country. Several months ago, National Geographic se…

Adding 2-digit numbers without regrouping 1 | Addition and subtraction | 1st grade | Khan Academy

Try to pause the video and figure out what 71 plus 24 is. All right, now let’s do this together. So let’s think about what 71 actually means. Well, we have a one in the ones place. Let me make this clear. So this is the ones place and we have one one. So …

Recognizing quadratic factor methods

We have other videos on individual techniques for factoring quadratics, but what I would like to do in this video is get some practice figuring out which technique to use. So, I’m going to write a bunch of quadratics, and I encourage you to pause the vide…

How to subtract mixed numbers that have unlike denominators | Fractions | Pre-Algebra | Khan Academy

More Articles