My Math Forum  

Go Back   My Math Forum > High School Math Forum > Algebra

Algebra Pre-Algebra and Basic Algebra Math Forum


Reply
 
LinkBack Thread Tools Display Modes
July 29th, 2011, 09:52 AM   #1
 
Joined: Jul 2011

Posts: 1
Thanks: 0

Calculate x as a % of y?

Hi,

can anyone tell me how to calculate x as a % of y? For example What % is 31 million of 72 million, for example?

Thanks guys, sorry if this sounds dumb! I'm learning!

Z
zudecke is offline  
 
July 29th, 2011, 01:06 PM   #2
 
Joined: Jul 2011

Posts: 227
Thanks: 0

Re: Calculate x as a % of y?

What's 1% of 72 million?...
Siron is offline  
July 29th, 2011, 08:13 PM   #3
Global Moderator
 
MarkFL's Avatar
 
Joined: Jul 2010
From: St. Augustine, FL., U.S.A.'s oldest city

Posts: 11,806
Thanks: 265

Math Focus: The calculus
Re: Calculate x as a % of y?

I would rewrite the question as follows:

What percentage of y is x?

Then translate the question into an equation as follows:

"What" is z (the unknown)

"percentage" is /100

"of" is (multiplication)

"y" is y

"is" is = ("is" is short for "is equal to")

"x" is x

Now, putting it together, we have:

(z/100)y = x

Solve for z by multiplying both sides by 100/y

z = 100(x/y)

So we see that when we want to know what percentage x is of y, we simply divide x by y then multiply by 100.
MarkFL is offline  
July 30th, 2011, 08:12 AM   #4
 
Joined: Jul 2011

Posts: 245
Thanks: 0

Re: Calculate x as a % of y?

You could also think:



Percentage is actually an 'operator'. . . I didn't realize this (I was very lackadaisical in my intuitive side of math. . .) until a while back.

Basically, a percentage sign means:



This is because of the equality:



Interestingly enough, it turns out that percentage is--like all mathematical operators--a convention of sorts to simplify an expression. I think that's pretty cool--the entire world uses a mathematical operator without necessarily knowing what it means. xD
CherryPi is offline  
July 30th, 2011, 10:19 AM   #5
Global Moderator
 
greg1313's Avatar
 
Joined: Oct 2008
From: London, Ontario, Canada - The Forest City

Posts: 6,087
Thanks: 311

Math Focus: Elementary mathematics and beyond
Re: Calculate x as a % of y?

31/72 ? .4305 ? 43.05%.
greg1313 is offline  
July 30th, 2011, 08:11 PM   #6
 
Joined: Apr 2011
From: USA

Posts: 782
Thanks: 1

Re: Calculate x as a % of y?

I look at this in a much different manner. I find most people don't have too much trouble learning how to find x% of some other number, which is just a multiplication.

i.e. what is 10% of 2100: 2100 * .10 = 210. (And refer to CherryPi's post about why you're moving that decimal over twice. A lot of people seem not to realize that a percent means parts out of 100.)

That is giving us what is 10% of the 2100.

If you already have the 210 and want to know what percent that is of the 2100, it means you have the "answer" to the above equation and it becomes 2100 * x = 210. The percent is missing. If we multiply to go forward, we start with the "answer" and divide to go backwards: 210/2100 = .10. (That will give the decimal version. You have to move it back over twice to put it back into a percent form of 10%.) So any time you want to know what percent x is of y, divide in that order: x/y.

If you have the 210 and the 10% and you want to know what the original number was, then that's like this:
x * .10 = 210. Again, to go backwards we divide: 210/.10 = 2100. So if you already have the portion of some other number and you want the original number, that is, x is y percent of what original number, again you divide in that order.

Or you can learn it this way: Base = 2100, Rate = 10% and Part = 210. When doing a division, the part always come first in the division.
Erimess is offline  
Reply

  My Math Forum > High School Math Forum > Algebra

Tags
calculate



Search tags for this page
Click on a term to search for related topics.
Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to calculate!!!! sajjad mt Calculus 12 December 2nd, 2013 09:25 AM
Calculate x Chikis Algebra 4 June 13th, 2013 09:03 PM
To calculate the value of Z pitrpan Advanced Statistics 2 April 14th, 2011 01:09 PM
calculate 1^2+2^2+...n^2 stole Number Theory 3 August 15th, 2009 06:41 AM
how calculate Espanol Algebra 3 April 2nd, 2009 10:03 PM





Copyright © 2014 My Math Forum. All rights reserved.