percent increase/decrease

[atl]

i don't understand percent increase/decrease questions...
I learned 2 ways to do this,
method 1. Subtract the original value from the new value, divide that by the original value, convert that to a percent (multiply by 100)
method 2. Divide the new value by the original value, convert that to a percent, subtract 100%? (if it's over 100%? i don't really get that part either)

but with most problems, those two methods will give me two different answers, and one of them is right and one is wrong.

example.. What is the percent increase if 15 increases by 9? Using the first method, -6 / 15 = 0.4, I end up with -40%, but that's wrong. The second method gives 60% which is right (but if I subtracted 100%, it would also be -40%?)
But with some other problems, method 1 gives the right answer and method 2 is wrong.
what am i doing wrong here?

 

[JeffM]

i don't understand percent increase/decrease questions...
I learned 2 ways to do this,
method 1. Subtract the original value from the new value, divide that by the original value, convert that to a percent (multiply by 100)
method 2. Divide the new value by the original value, convert that to a percent, subtract 100%? (if it's over 100%? i don't really get that part either)

but with most problems, those two methods will give me two different answers, and one of them is right and one is wrong.

example.. What is the percent increase if 15 increases by 9? Using the first method, -6 / 15 = 0.4, I end up with -40%, but that's wrong. The second method gives 60% which is right (but if I subtracted 100%, it would also be -40%?)
But with some other problems, method 1 gives the right answer and method 2 is wrong.
what am i doing wrong here?

Method 1 and method 2 will always give you the same, correct answer if you perform them both correctly.

Let's take your example problem. And do it step by step OK

If 15 is the original value and it is increased by 9, what is the new value?

 

[atl]

Ok I just realized after posting that, that I forgot to add the two numbers first I got confused because of different problems being worded differently, I had done

some others where the second number they give you is the new value so yeah. Thanks for pointing that out, I have to pay more attention to the questions...
15 + 9 = 24 ... 24 - 15 = 9 .... 9 / 15 = 0.6, it's 60%
or 24 / 15 = 1.6 = 160% - 100% = 60%
yay!

 

[lookagain]

15 + 9 = 24 ... 24 - 15 = 9 .... 9 / 15 = 0.6, it's 60%


or 24 / 15 = 1.6 = 160% - 100% = 60%\(\displaystyle \ \ \ \ \)<---This train of equalities is false. You must split them up,
as was done with the suggested steps below.

24/15 = 1.6

1.6 = 16/10 = 160/100 = 160% \(\displaystyle \ \ \ \ \)<---- These are my own optional intermediate steps.

160% - 100% = 60%