Subtracting a fraction from a whole number
About this video
The video finds 6 - 3/4 in two ways. First it rewrites 6 as 24/4 and subtracts to get 21/4. Then it splits 6 into 5 + 1, rewrites the 1 as 4/4 and subtracts 3/4 to get 5 1/4, and shows that 5 1/4 and 21/4 are the same.
You'll be able to
- rewrite a whole number as a fraction with a given denominator.
- subtract a fraction from a whole number.
- show that a mixed number like 5 1/4 equals a fraction like 21/4.
Key words
- fourths
- The four equal parts a whole is split into; 4/4 makes one whole.
- mixed number
- A whole number and a fraction together, like 5 1/4.
- whole
- One complete thing; here it is 4/4.
Transcript
- [Instructor] Let's say we wanted to figure out what six minus 3/4 is equal to. Pause this video and work through this on your own before we work through this together. All right, now there's a couple of ways that we could think about this. The first way is we could represent this six wholes as a bunch of fourths.
So how many fourths is six wholes? Well, we already know that one is equal to 4/4. So six wholes, that's gonna be six times as many. So instead of 4/4, you're going to have 24/4. So, 24/4 is the same as six. And you could see that because you're going to use 4/4 for a whole.
And you could do that six times. And now, we can subtract the 3/4 from that. And what does that get us? Well, if I have 24 of something minus three of something, that's going to be 21 of that something. So, 24/4 minus 3/4 is 21/4. Now, there's another way that you could think about this.
You could say, well, six is the same thing as five plus one. And you might say, why would I do that? Well, if you have one here, you could subtract 3/4 from that. So you could subtract three, lemme do that in a different color. You could subtract the 3/4 now from the one.
And so this is going to be equal to five plus, and let's rewrite one over here. Lemme just do it in a different color. I'm having trouble changing colors today. One is how many fourths? Well, we already wrote it over here. It's 4/4. So that's 4/4 minus 3/4. And what is that going to be equal to?
Well, that's going to be equal to, once again, we have this five over here plus 4/4 minus 3/4 is, of course, this is going to be one. This over here is going to be 1/4. So you get five plus 1/4 is going to be equal to five and 1/4. You might say, hey, is that the same thing as 21/4?
Well, yes it is because five is what? That's the same thing as 20/4. So it says 20/4 plus 1/4, which is 21/4. Another way you could think about this, if you were to take four, it goes into 21 five times with a remainder of one. So there's many different ways that you could approach this.
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