Understanding Percent

What does per cent mean? Per means one. Cent is one penny out of a dollar.

A percent is a portion of a whole. How many parts do you need to start with ? You need 100 parts.

Let’s talk about money How many pennies are in a dollar? There are 100 pennies in a dollar.

Since there are 100 pennies, I could easily find any percent. 25% would be 25 out of 100 pennies. That would be 25₵. You can also write this as 0.25 or .25

12% would be 12 out of 100 pennies. That would be 12₵. You can also write this as 0.12 or .12

Let’s think about 2.00. To make 100 equal groups, how many pennies would be in each group?

There would be 2 pennies in each group.

So if I wanted to find 18% of 2, that would be 18 boxes. Since there are 2 pennies in each box, it would be a total of 36 pennies or 36₵. You can also write this as 0.36 or just .36

What if you had $5.00? How many pennies could be in each box?

All those pennies won’t fit in my picture, so let’s use tally marks.

Each mark stands for 1 penny.

So there is 5₵ in each box. We can write that as .05 per box.

So if I wanted to know 37% of $5.00, I would have to add .05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05++.05+.05+.05+.05+.05+.05+.05 = ?

Can you think if an easier way? .05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05+.05++.05+.05+.05+.05+.05+.05+.05 = ?

Multiply!!! 37 boxes X .05 per box 185 There are 2 digits after the decimal, so there needs to be 2 digits after the decimal in your answer. 185. = 1.85

Do you notice any patterns? Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 Do you notice any patterns?

Who can tell me how many pennies if I had…. Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 Who can tell me how many pennies if I had….

Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 $20

Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 $20 20

Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 $20 20 .20 or .2

Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 $20 20 .20 or .2 $87

Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 $20 20 .20 or .2 $87 87

Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 $20 20 .20 or .2 $87 87 .87 $99

Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 $20 20 .20 or .2 $87 87 .87 $99 99

Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 $20 20 .20 or .2 $87 87 .87 $99 99 .99

Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 $20 20 .20 or .2 $87 87 .87 $99 99 .99 $112

Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 $20 20 .20 or .2 $87 87 .87 $99 99 .99 $112 112

Total # of pennies in each box Written as a decimal $1.00 1 .01 $2.00 2 .02 $5.00 5 .05 $20 20 .20 or .2 $87 87 .87 $99 99 .99 $112 112 1.12

When you are calculating percent, you are Splitting the whole into 100 equal parts (moving the decimal 2 places to the left) Then adding (or multiplying) the required number of parts out of 100 17% of 63 Split 63 into 100 equal parts by moving the decimal .63 You need 17 out of 100 parts. Each part is worth .63 17 ● .63 = 10.71 17% of 63 is 10.71

The communitive rule of multiplication allows us write the percent as a decimal instead. Write 17% as a decimal (move the decimal 2 spaces to the left) .17 .17 ● 63 = 10.71 17% of 63 is 10.71

One last example: 84% of 126 84 ● 1.26 = 105.84 OR .84 ● 126 = 105.84