Transcript Decimals (Concepts & Computation)

Percent
(Concepts & Computation)
Dec. 2
Introducing Percent
• Percent is a ratio of a number to 100.
• The symbol for percent is %
• Percent means “per hundred”
•
17
• So, ------- is 17%
•
100
•
Finding Percents and
Decimals
•
27
• Ratio; ----•
100
• Percent; 27%
• Decimal; 0.27
• To write a percent as a decimal, move
the decimal point two places to the
left. Drop the percent sign.
– 51% = 51. = 0.51
– 2% = 02. = 0.02
– 15.6% = 15.6 =0.156
• To write a decimal as a percent, move
the decimal point two places to the
right, write the percent sign.
– 0.82 = 0.82 = 82%
– 0.03 = 0.03 = 3%
– 0.319 = 0.319 = 31.9%
Exercise
• Write each percent as a decimal
• 63% = 63. = ___ 6% = 06. = ___
• 22.3% = 22.3. = ___
• Write each decimal as a percent
• 0.66 = 0.66 = ___ 0.02 = 0.02 = ___
• 0.163 = 0.163 = ____
Percents and Fractions
To find the percent for any fraction,
you can divide the numerator by the
denominator to find the decimal.
• Then you can write the percent
– Find the percent for ½
– Divide 1 by 2 = 0.5
– 0.5 = 50%
Exercise
• Write as fraction, whole numbers, or
mixed numbers. Show the answers in
lowest terms.
– 1%
70%
400% 150%
57%
89%
• Write as percents.
•
•
•
9
---100
67
---100
3
--10
4
---25
3
1 --20
175%
Finding Percent using Mental Math
percent fraction
think
example
200%
2/1
Multiply by 2
200% of 10
100%
1/1
Multiply by 1
100% of 3
50%
½
25%
¼
10%
1/10
Multiply by ½ 50% of 8
or divide by 2
Multiply by ¼ 25% of 16
or divide by 4
Multiply by
10% of 460
1/10 or divide
by 10
Exercise
•
•
•
•
•
•
200% of 60
25% of 12
10% of 30
100% of 15
200% of 20
10% of 210
5% of 540
50% of 50
12% of 100
80% of 40
50% of $16.50
50%
25%
75%
75%
of 28
of 32
of 84
of $24