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UNITS
Unit 2A
The units of a quantity described what is being
measured or counted.
NOTES:
The Problem-Solving Power of
Units
• To add or subtract quantities, the units must
be the same. “You cannot add apples and
oranges.”
• Quantities with different units can be
multiplied or divided.
READING UNITS
Key Word
Example
or Symbol
“miles per hour”
Division
per
(miles ÷ hour)
“square feet” or “feet squared”
Raising to
square
(ft × ft or ft2)
second power
Raising to
cube or
“cubic feet” or “feet cubed”
third power
cubic
(ft × ft × ft or ft3)
“kilowatt-hours”
Multiplication hyphen (kilowatts × hours)
Operation
UNIT CONVERSIONS
To convert from one unit (say “old ”) to another
unit (say “new ”), we multiply by a conversion
factor in an equivalent form of 1, whose
denominator has “old ” units and whose
numerator has “new ”units.
The “old ” units will cancel.
EXAMPLES OF UNIT
CONVERSION
1. 7 days = 1 week has unit conversions.
1=
7 days 1 week
=
1 week 7 days
(a) Convert 28 days to weeks.
(b) Convert 28 weeks to days.
4. A vacant lot has an area of ¾ acre. What
is its size in square feet?
(1 acre = 43,560 ft2)
5. A car is driving at 75 miles per hour. What
is its speed in miles per minute?
2. How many inches are in 9 feet?
3. Convert 160 oz to lb.
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USING A CHAING OF
CONVERSIONS
CONVERSION WITH UNITS
RAISED TO A POWER
1 yd 2 = 1 yd × 1 yd
= 3 ft × 3 ft
= 9 ft 2
2. How many seconds are there in 2 days?
3. Convert 15 miles to yards.
4. Convert 3 weeks into seconds.
1 ft 2 = 1 ft × 1 ft
= 12 in × 12 in
= 144 in 2
1. Convert 6 ft2 to in2.
2. Convert 2000 in2 to ft2.
3. Convert 99 ft2 to square yd.
4. Convert 108 yd2 to square ft.
5. How many cubic yards of soil are needed to
fill a planter that is 20 feet long by 3 feet
wide by 4 feet tall?
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