About this video
The video turns word statements into algebraic subtraction expressions. 'Two less than x' becomes x - 2, 'y fewer than three' becomes 3 - y, and 'x decreased by five' becomes x - 5. The key idea is to think about what you start with, because the order of the words is not always the order you write them.
You'll be able to
- write a subtraction expression from words like 'less than', 'fewer than' and 'decreased by'.
- explain why 'two less than x' is x - 2, not 2 - x.
Key words
- algebraic expression
- A maths phrase that uses numbers, letters (variables) and operations, like x - 2.
- variable
- A letter, like x or y, that stands for a number.
- less than / fewer than
- Words that mean subtract from the second amount: 'two less than x' means x - 2.
- decreased by
- Made smaller by an amount: 'x decreased by five' means x - 5.
Transcript
- [Instructor] We have different statements here that can each be expressed as an algebraic expression, and as you might have guessed, I would love you to pause this video and try to write each of these statements as an algebraic expression before we do it together.
All right, now let's work on it together. So this first statement, we have two less than x. So my brain thinks, all right, let me start with x, and how am I going to get two less than that? Well, I'm going to subtract two. And this is an interesting example because you see the order that we see it in the sentence is not the order that we would necessarily write it in the expression right over here.
Very important to think about, what is going on here? What is being described? Now, this next statement, y fewer than three. Well, in my mind, I'm going to start with three and I'm going to be y fewer than that. So I'm gonna start with three and then I'm going to be y fewer than that.
Now, these first two statements are similar in that you have something less than something else or something fewer than something else. They just swapped the number and the variable. Now, this third statement, x decreased by five. So my mind is thinking, what am I starting with?
I'm starting with an x and I'm decreasing it by five. So I can do that as minus five, or I'm gonna take five away from it.
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