About this video
This video subtracts 7 6/9 - 3 2/5. It splits each mixed number into whole and fraction parts, subtracts 7 - 3 = 4, then uses 45 as the common denominator so 6/9 - 2/5 = 30/45 - 18/45 = 12/45. Finally it simplifies 12/45 by dividing by 3 to get 4 4/15.
You'll be able to
- subtract mixed numbers by subtracting the whole parts and the fraction parts.
- find a common denominator for 9 and 5 and subtract the fractions.
- simplify a fraction answer by dividing by a common factor.
Key words
- mixed number
- A whole number and a fraction together, like 7 6/9.
- least common multiple
- The smallest number both denominators divide into; for 9 and 5 it is 45.
- common factor
- A number that divides evenly into two numbers, like 3 for 12 and 45.
- simplify
- Divide the top and bottom by a common factor to write the fraction more simply.
Transcript
- [Instructor] Let's try to evaluate 7 6/9 - 3 2/5. So like always, I like to separate out the whole number parts from the fractional parts. This is the same thing as 7 at + 6/9 - 3 - 2/5. And the reason why I'm saying - 3 - 2/5 is this is the same thing as - (3 + 2/5).
And so you distribute the negative sign, you're subtracting a 3, and then you're subtracting the 2/5. And so now we can worry about the whole number parts, 7 - 3. Well, 7 - 3 is going to give us 4. So that's going to give us 4. And then we're going to have 6/9 - 2/5.
So let me think about what 6/9 - 2/5 are. 6/9 - 2/5. Well, we're gonna have to find a common denominator. So this is going to be the same thing. And I think the least common multiple of nine and five is going to be 45. Literally, they multiply, they have no common factors.
It's gonna be over 45, to go from 9 to 45 I had to multiply by 5. So I'm gonna have to multiply the numerator by 5. So 6 x 5 is 30, and I'm gonna subtract. To go from 5 to 45, I had to multiply by 9. So I have to multiply the numerator by 9 if I don't wanna change the value.
So 2 x 9 is 18 and 30 over, 30/45 - 18/45, it's gonna be something over 45, 30 - 18 is 12. So this is, if I subtract these two fractions right over here, I get 12, 12/45. So it's 4 + 12/45. Or if we wanted to write it as a mixed number, this is equal to 4 and 12/45, but we're not done yet.
We can simplify this further. 12 and 45 have common factors. They're both divisible by, they're both divisible by three. So we can say that this is, actually, they're both divisible by, yep, well, I think we can divide more after that. So let's see. If we divide the numerator by three and the denominator by three, we end up with 4 and 12 divided by 3 is 4 and 45 divided by 3.
45 divided by 3 is 15. 4 4/15 and actually we're done. These two can't be simplified anymore. 4 4/15.
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