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## Algebra (all content)

### Course: Algebra (all content)ย >ย Unit 11

Lesson 10: Exponential expressions

# Exponential expressions word problems (algebraic)

Given a real-world context that involves repeated multiplication, we model it with an exponential function.

## Want to join the conversation?

• at in the video, how do you figure you can add 1 to .3?
• When something increases by 30%, then you have the original amount, which is 100% + 30%
Change those into decimals and you get 1 + 0.3 = 1.3
• Can someone please explain the factoring part? Why does it result in 1? Thank you!
• he wrote 170(1+0.3) where the 1 come from?
• As stated in other responses to nearly the same question...
If something grows by 30%, you have the original amount (100%) + the new amount (30%).
If you change these into decimals you get: 100% = 1 and 30% = 0.3
This is where the 1+0.3 comes from.
Hope this helps.
FYI... get in the habit of reading the other questions and answers. They may answer your question and/or give you new insights into the problem.
• When exponential expressions were first introduced in Khan Academy, I was able to write them like this:

170(1 + 0.3)^t

But now I'm told to write them like this:

170(1.3)^t

And the former version is marked wrong. Why? Is it just to simplify the expression because I've learned the concept?

Edit: Turns out the first version isn't marked wrong, but I'm still wondering why the second is encouraged.
• When I see this on tests at school, the second is almost always the ABCD option, I guess the reason is what you say, it is the simplified version.
• what if the percent is 0
(1 vote)
• If the percentage is 0, then there's no increase in the population, so basically there's no need to calculate anything. ;)
• It really helped
• I have a question:
When can we know if our growth rate should be added by 1 or not? For example in the video, Sal added 100% to the increasing growth rate of 30%. Does this always happen in every word problem example?

Sorry if my question is hard to understand, but I'm hoping for someone to answer my question soon. I'm open to answering anyone that needs more clarification for my question! Thx :)
• If the problem gives you the percent increase, then you start with the original amount (100%) and add the increase (30%) = 130%

If the problem gives you a percent decrease, then you start with the original amount (100%) and subtract the decrease (30%) = 70%

Hope this helps.
• why aren't you using any of the formulas? it will make it a lot easier for us to understand.
(1 vote)
• Hi, Hana B!
Formulas are a handy thing to use, but Sal is trying to explan the principals behind the formula. In my opinion, knowing the mechanics is much more important than just memorizing the formula.

Hope that helped!