Basic HTML Version
© 2014 Pacific Crest
85
Step
Watch it Work!
3. Substitute given values
for the variables
50 miles 90 minutes
1 hour
d r t
d
=
=
4. Simplify units
no units to simplify
5. Convert to same units
50 miles
1 hour
90 min
1 hour
60 min
d
=
6. Simplify units
50 miles
1 hour
d
=
90 min
1 hour
60 min
7. Perform all operations
75 miles
d
=
8. Validate your answer
and its units
(
)
(
)
75 miles
75 miles
90 minutes
75 miles
75 miles
90 minutes 90 minutes
5 miles 5 miles 60 minutes
6 minutes 6 minutes
hour
5 miles
6 minutes
d
rt
r
r
r
r
=
=
=
=
=
=
=
=
60 minutes
5 60 miles
miles
50
hour
6 hour
hour
=
=
YOUR
TURN!
Scenario:
Find the speed of a car in kilometers per hour, if it is driving at 1 mile per minute
O
ops
! A
voiding
C
ommon
E
rrors
●
Not calculating/validating both the value and the unit
Example
: What is the area of a rectangle that is 4 feet wide and 9 feet long?
A
=
width
×
length
A
= 4 × 9 =
36
A
=
width
×
length
A
= 4 ft × 9 ft =
36 ft
A
=
width
×
length
A
= 4 ft × 9 ft =
36 ft
2
incorrect
(units left out)
incorrect
(units not calculated)
correct
(feet × feet = square feet)
Why?
Answers that have units must contain both the number and the unit. This means that
both must be calculated and validated. If the correct answer to a problem is “30 miles
per hour,” an answer of “30” is as incorrect an answer as “30 kilometers per hour” is.
2.3 Evaluating a Formula