Half. Because 50 is half of 100.
A quarter, or a fourth. Because 25 is a quarter of 100.
Two times, or twice as much. Because 200 is two times 100.
Ten times. Because 1000 is ten times 100.
Example 9. How much is 10% of $434?
Translate: "How much is a a tenth of $475?" (10% means a tenth, because 10 is a tenth of 100.) To find a tenth of a number, divide it by 10. To divide a whole number by 10, separate one decimal place:
$434 ÷ 10 = $43.4
Money however is written with two decimal places. Therefore report the answer as
$43.40.
Example 10. How much is 20% of $142?
Answer. 20% is twice as much as 10%. 10% is $14.20. Therefore 20% is $28.40.
The Base
Example 11. 7 is 25% of _?_
Answer. The Base -- the number that follows of -- is missing.
Translate:
"7 is a quarter of what number?"
7 is a quarter of 28.
Example 12. 10 is 20% of _?_
Translate: "10 is the fifth part of what number?" (20% means the fifth part, because 20 is the fifth part of 100.)
10 is the fifth part of 50.
Example 13. 15 is 300% of _?_
Translate: "15 is the three times what number?"
15 is three times 5.
Example 14. 280 is 1000% of _?_
Translate: "280 is the ten times what number?"
280 is ten times 28.
(Lesson 3, Question 1.)
The Percent
Example 15. 48 is what percent of 48?
Answer. 100%. 100% is the whole thing!
Example 16. 9 is what percent of 36?
Answer. To ask
is the same as asking
Percents are ratios.
Now,
9 is a fourth of 36.
Therefore,
9 is 25% of 36.
25% means a fourth, or a quarter.
Example 17. 35 is what percent of 7?
Translate: "35 has what ratio to 7?"
35 is five times 7.
The percent, then, will be five times 100:
35 is 500% of 7.
In every case,
The percent has that same ratio to 100.
Example 18. $2.50 is what percent of $250?
Answer. "$2.50 is which part of $250?"
The digits are the same: 2, 5, 0. But $2.50 has two decimal places. It is $250 divided by 100:
2.50 = 250 ÷ 100.
Therefore,
$2.50 is 1% of $250.
(Example 7 above.)
At this point, please "turn" the page and do some Problems.
or
Continue on to the next Section.
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