SME
Grade 9 Math · Problem type
Units in a formula: d = rt
Use this for “A cyclist rides at 18 km per hour for 40 minutes. How far does she go?”
Diagram
tₕ = 2/3 h on the top line sits over 12 km on the bottom line: each 1 above is 18 below.
This is an example. Type your own values to start a new problem.
d (km)
=
r (km/h)
×
t
min
×
1
h
60
min
tₕ
Time in hours
worked out (not typed) · h
Formulas
tₕ
=
t
60
2
3
=
40
60
d
=
r
×
tₕ
12
=
18
×
2
3
Assumptions
•
The rate is per hour, so the time must be in hours before multiplying.
•
Divide minutes by 60 to get hours: 30 min is 1/2 h.
•
Kilometers per hour times hours leaves kilometers: the hours cancel.
Step-by-step
WE KNOW
r = 18 km/h, t = 40 min
FIND
time in hours (tₕ), distance (d)
Step 1 · Find time in hours (tₕ)
Use tₕ = t ÷ 60
An hour is 60 minutes, so divide by 60 to write the time in hours, as the rate is.
tₕ
=
40
60
tₕ
=
2
3
h
Step 2 · Find distance (d)
Use d = r × tₕ
Distance per hour times hours: the hours cancel, leaving the distance.
d
=
18
×
2
3
d
=
12
km
Check
Put the numbers back in. Both sides should match.
2
3
=
40
60
✓
12
=
18
×
2
3
✓
Topic check
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