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Objective
Compute mentally with percents
Example 1 Use Fractions to Compute Mentally
Example 2 Use Fractions to Compute Mentally
Example 3 Use Decimals to Compute Mentally
Example 4 Use Decimals to Compute Mentally
Example 5 Use Proportion to Solve a Problem
Compute 40% of 80 mentally.
4 8
Write the problem40% of 80Remember “of” means multiplication
00
Bring down the zeros
Remember % means 100 so to take away the % sign divide by 100
3200100
Answer: 32
1/5
Multiply the 4 832
Since there are 2 zeros in both numerator and denominator, cancel them out
32
Compute 20% of 60 mentally.
Answer: 12
1/5
Compute of 75 mentally.
70%
Write problem66 % of 752
3 Round to easy number
70
2/5
is about 70%
75 is about 70 or 80 (either will work)
Remember: of means to multiply
Compute of 75 mentally.
70%
66 % of 7523
70
2/5
Multiply the 7 7
7 749
Bring down the zeros
00
Remember % means 100 so to take away the % sign divide by 100
100 Since there are 2 zeros in both numerator and denominator, cancel them out49Answer:
Answer: 210
Compute of 300 mentally.
2/5
Compute 10% of 65 mentally.
3/5
Write problem10% of 65
Round to easy number
10% is already an easy number
10%
Remember: of means to multiply
10%
65 is about 60 or 70 (either will work)
70
Compute 10% of 65 mentally.
3/5
10% of 65
10% 10% 70
Multiply the 1 7
1 7
Bring down the zeros
700
Remember % means 100 so to take away the % sign divide by 100
100Since there are 2 zeros in both numerator and denominator, cancel them out
7Answer:
Answer: 1
Compute 10% of 13 mentally.
3/5
Compute 1% of 304 mentally.
4/5
Write problem1% of 304
Round to easy number
1% is already an easy number
1% 1%
Remember: of means to multiply
304 is about 300
300
Answer:
Compute 1% of 304 mentally.
4/5
1% of 304
1% 1% 300
Multiply the 1 3
1 33
Bring down the zeros
00Remember % means 100 so to take away the % sign divide by 100100Since there are 2 zeros in both numerator and denominator, cancel them out
3
Answer: 2.5
Compute 1% of 244 mentally.
4/5
TECHNOLOGY A company produces 2,500 of a particular printer. They later discover that 25% of the printers have defects. How many printers from this group have defects?
Remember: Part = % Whole
5/5
Define the variable: How many printers are defective
Since all the printers are not defective, need to find the part
x
How many printers from this group have defects
Convert 25% to a decimal
x = 0.25
TECHNOLOGY A company produces 2,500 of a particular printer. They later discover that 25% of the printers have defects. How many printers from this group have defects?
Company produces 2,500 which is the total number of printers
5/5
x
How many printers from this group have defects
x = 0.25x = 0.25 2,500
Since the variable is by itself, multiply 0.25 2,500
x = 625
Add dimensional analysis
x = 625 defective printers
Answer: 625 printers had defects
TECHNOLOGY A company produces 1,400 of a particular monitor. They later discover that 20% of the monitors have defects. How many monitors from this group have defects?
Answer: 280 defective monitors
*
5/5