Chapter 4.3 Proportions and Percent Equations

 Percent- this is a ratio that compares a number to 100, or 100%.

    Part     =      %                         is    =    %   

  Whole          100                        of         100

* In an equation the the number after is, is the Part. And the number after of is the Whole.

Here are some examples, write a proportion to solve.

 

 

What % of 24 is 9?

 

 

 

 

***In a problem like this--the What is ALWAYS your variable because we don't know what it is.***

 

                                                                                 9     =    X   

You should come up with something like this---->   24         100  

 

 

The way to solve this is that you get your proportion then cross multiply and divide the number with X.

 

When cross multiplied it looks like this--->    24x=900      If you divide the 24 you will find the answer.

 

Answer is  X=37.5

 

Try it by yourself now-

 

 

What % of 53 is 34?

 

1. Set up your proportion
2. Cross multiply
3. Then Divide the number with X

 

 

 

 Writing an equation             (is--> =, of--> *)

 

 

Here's an example

 

What %(X) of(*) 67 is(=) 43?

 

It should look like this-----> 67x=43

 

All you have to do now is divide the 67 or the number multiplied by x.  

 

67/67x=43/67

 

 

The answer is-->x=.64  ***(If the variable is a % then move the decimal 2x's to the right.)***

 

 

 

 

Here are some helpful values when estimating--                             

percent--5%    10%     20%   25%   33%   40%   50%    60%    66.6%   75%   80%   90%

fraction--1/20  1/10     1/5     1/4     1/3     2/5     1/2      3/5        2/3      3/4     4/5     9/10

 

 

When you are trying to figure out the part with only the whole and percent it may help to round to the closest fraction above and round the whole to the nearest value of 10 (like 250,120,360 etc...)

 

Here are some examples:

 

 

Estimate each value

 

 

A.   34% of 267

 

 

You would start to solve this problem by rounding.

 

When you are done rounding your equation should look like this--> 1/3*270

 

Then it's a matter of multiplication from here on out

 

1/3*270=89.1

 

 

 

 

Try this one on your own-->   42% of 143

 

 

 

The equation is--> 2/5*140=

 

 

Here's the answer--> 56