Marna's house is 22 miles from where she works. Each morning, she jogs at a rate of 6 mph to a bus stop and then completes the trip on a bus that averages 30 mph. If the entire trip takes 1 hour, how much time does Marna spend jogging?
Make this chart:
distance = rate × time
from home to bus stop jogging | | | |
from bus stop to work riding | | | |
totals riding & jogging | | | |
Let x be the answer. So we fill in x for the time from home to
the bus stop jogging
distance = rate × time
from home to bus stop jogging | | | x |
from bus stop to work riding | | | |
totals riding & jogging | | | |
Next we fill in the rates of 6 mph and 30 mph
distance = rate × time
from home to bus stop jogging | | 6 | x |
from bus stop to work riding | | 30 | |
totals riding & jogging | | | |
We fill in the total time of 1 hour
distance = rate × time
from home to bus stop jogging | | 6 | x |
from bus stop to work riding | | 30 | |
totals riding & jogging | | | 1 |
We fill in the total distance of 22 miles
distance = rate × time
from home to bus stop jogging | | 6 | x |
from bus stop to work riding | | 30 | |
totals riding & jogging | 22 | | 1 |
Use Distance = Rate × Time to fill in her distance jogging to the
bus stop from home.
distance = rate × time
from home to bus stop jogging | 6x | 6 | x |
from bus stop to work riding | | 30 | |
totals riding & jogging | 22 | | 1 |
Use the principle:
Time riding = Total time riding and jogging - time jogging
to fill in the time from the bus stop to work riding the bus as 1-x.
distance = rate × time
from home to bus stop jogging | 6x | 6 | x |
from bus stop to work riding | | 30 | 1-x |
totals riding & jogging | 22 | | 1 |
Fill in the distance riding the bus using
distance = rate × time
distance = rate × time
from home to bus stop jogging | 6x | 6 | x |
from bus stop to work riding | 30(1-x) | 30 | 1-x |
totals riding & jogging | 22 | | 1 |
Now we form the equations from the principle:
Distance jogging + Distance riding = Total distance jogging and riding:
6x + 30(1-x) = 22
Solve that and get x = of an hour or =
20 minutes jogging and 40 minutes riding.
So the answer asked for is 20 minutes jogging.
Edwin