Writing expressions for a percent increase
At about 83s the narrator says B + 30B 'is not one of the choices' when it is listed; he means it is not a correct choice. Minor slip.
The check-ins use the correct version. The video is Khan Academy's, unchanged.About this video
The video writes expressions for an amount B that is increased by an additional 30%. It shows that B + 0.3B and 1.3B both give the new total, and explains why B + 30B and 0.3B do not.
You'll be able to
- write an expression for an amount increased by a percent.
- show that B + 0.3B and 1.3B are equivalent.
- spot expressions that give only the increase, or use the percent wrongly.
Key words
- Percent increase
- Adding a percent of the original amount on top of the original amount.
- Equivalent expressions
- Expressions that look different but always give the same value.
- Factor out
- Pull a common factor, like B, out of each term: 1B + 0.3B = (1 + 0.3)B.
Transcript
- [Instructor] Ms Naveen's class collected B blankets for the animal shelter. Then they collected an additional 30% of that amount. Select all the expressions that give the total number of blankets Ms. Naveen's class collected. Choose two answers. All right, pause the video, like always, and see if you can pick those two answers.
Okay, so I'm not gonna even look at the choices. I'm just gonna try to reason it through. That's one way to approach it. So in the class, they collected B blankets, then they collected an additional 30% of that amount, so then they collected an additional 30% of B.
So this is one way to write it. Maybe you could also write it this way, B plus 0.30B. This is just another way of writing 30%. Or another way to write it is you could factor out a B, because this is the same thing as 1B plus 0.30B. So, you could say this is the same thing as one plus 0.30B, which is the same thing as 1.3B.
Now, let me look at the choices and see which of these are consistent with everything I just wrote here. So B plus 30B, if this was 30% maybe, but not 30, that's going to be a huge number. This is not one of the choices. B plus 0.3B, well, that's what I had originally written right over here.
You have B, plus an additional 30% of that amount, so I definitely like this one. 0.3B, now, that would just be 30% of the original amount. That's not the total amount that we now have now, so we'll rule that one out. And this last one is exactly what we got when we essentially rewrote this one, when we added 1B plus 0.3B, so we got 1.3B, so I like those two choices.
Video © Khan Academy, used under CC BY-NC-SA. Watch on Khan Academy. Puzzicle is not affiliated with Khan Academy.