Writing expressions for a fraction of a quantity
About this video
A soccer team collected d kilograms of dog food and donated 1/3 of it. The amount left is d − 1/3 d, which can be rewritten as d(1 − 1/3) = 2/3 d. Both expressions are correct.
You'll be able to
- write an expression for what is left after taking away a fraction of an amount.
- rewrite d − 1/3 d as 2/3 d by factoring out d.
Key words
- expression
- A maths phrase with numbers, letters and operations, like d − 1/3 d.
- factor out
- Pull a common part, like d, outside brackets: 1d − 1/3 d = d(1 − 1/3).
Transcript
- [Instructor] The soccer team collected d kilograms of dog food. Later, the team donated 1/3 of that amount to a local animal rescue. Select all of the expressions that give the number of kilograms of dog food the soccer team has left after the donation. Pause this video. Have a go at that.
All right, so the team collected d kilograms. That's where we're going to start. And then the team donated 1/3 of that amount. So 1/3 of that amount is 1/3d, and they donated that. So whatever we started with, we're gonna subtract the amount that we donated and that's what we are going to have left after the donation.
So this is going to be equal to what? Well, we actually already see this expression as one of them. So we could say, okay, this is one way of expressing the amount they started with and then donating 1/3 of that. But what's another way to express it? Well, you could think of this as 1d - 1/3d.
And you could think of this as, or another way of rewriting this is if you were to factor a d out, you could say this is d times 1 - 1/3, which is equal to d times 2/3 or 2/3d. Or another way you could have thought about this is if you have 1d and you subtract 1/3 of that d, you're gonna have 2/3 of that d left.
And you can see that is choice A right over there.
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