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.

For Children With Clubfoot, Treatment Can Be Life Changing | Short Film Showcase

The Joke That Accidentally Became A 'Fact' @JoeKwaczala

View All

The development of an American culture | AP US History | Khan Academy

In this video, I’m going to take some time to talk about the culture of the young United States that developed in the early 19th century. At the beginning of this period, most of the dominant artistic and cultural productions in the United States—the pain…

More problems with knowing the 'fundamental nature' of X

Npg85 made a video in which he offered an alternative way of trying to distill the fundamental essence of the process. In his video, he used the example of a computer speaker to illustrate his thinking. So I’m going to use the same example to demonstrate …

Worked example: Derivative of cos_(x) using the chain rule | AP Calculus AB | Khan Academy

Let’s say we have the function f of x, which is equal to cosine of x to the third power. We could also write it like this: cosine of x to the third power. We are interested in figuring out what f prime of x is going to be equal to. So, we want to figure o…

Factors affecting acid strength | Acids and bases | AP Chemistry | Khan Academy

Factors that affect acid strength include bond polarity, bond strength, and conjugate base stability. Let’s think about a generic acid, HA, that donates a proton to water to form the hydronium ion, H3O⁺, and the conjugate base, A⁻. First, let’s consider …

Coulomb's law | Physics | Khan Academy

We encounter so many different kinds of forces in our day-to-day lives. There’s gravity, there’s the tension force, friction, air resistance, spring force, buoyant forces, and so on and so forth. But guess what? Not all these forces are fundamental. Gravi…

War with China?

You also talked about what you think is a potential war, frankly, either economic war, uh, or physical war between the U.S. and China, either over Taiwan or other things. Where do you think that sits in this calculus of yours? Well, we are, you know, the…

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

More Articles