Math 6High ( Period 3)

Large & Small  Percent 7.3

The methods you learned from Lesson 7.2 can be used to find large and small percents.

Rewrite Numbers

Rewrite 1.4 as a percent
1.4 = 1  4/10 = 14/10 = 140/100 = 140%

Rewrite   ½%  as a decimal
½ %= 0.5% = 0.5/100 = 5/1000 = 0.005

Finding a Large Percent of a Number

You can use either of two methods to find 130% of 250

Method 1: Set up a proportion      percent/100 = is/of

130/100 = x/250

Cross multiply carefully

(130)(250) = 100x  Then divide by 100 on both sides

(130)(250)/100 = 100x/100

325 = x

There were a number of different ways to simplify BEFORE you multiply but do them carefully . You still need to get x = 325

Method 2: Rewrite 130% as a decimal and set up a written equation

Find 130% of 250.   Think “ Find”  means “What is…” so you have

What is 130% of 250
x = (1.3 )(250)
x = 325

Find a Small Percent of a Number

You can use the same two methods to find 0.5% of 40

Method 1: Set up a proportion.

.5/100 = x/40  or

5/1000 = x/40

Cross multiply and divide carefully
(5)(40)/1000 = 1000x/1000

0.2 = x

There were a number of different ways to simplify BEFORE you multiply but do them carefully . You still need to get x = 0.2

Method 2: Rewrite 0.5% as a decimal and use the writing an equation method

Find 0.5% of 40   Think “ Find”  means “What is…” so you have
What is 0.5% of 40.
x = (0.005)(40)
x = 0.2

Estimating:

In many real-life situations—such as figuring the amount for a tip, it is helpful to use mental math to estimate the percent of a number.

Use mental math to estimate 123% of 84. You know it will be MORE than 84… because the percent is over 100% and we know 123%  is about 125%   100% + 25% so all we need to figure is 25% o 84… and that is just ¼ so 21.. 84 + 21 = 105. So 123% is just a little under 105.  

Use mental math to find ½ % of 140

Wait… ½ % is just half of 1% so  figure 1% of 140. Just move the decimal over two places…1.4 would be 1% so half of that is 0.7

estimate 15% tip for a restaurant bill of $43.76

First round the restaurant bill up to $45.00. Then take 10% … that’s 4.50

5% is half of ten percent so half of 4.50  is 2.25

4.50 + 2.25 = 6.75  $6.75 is about 15% of43.76