SOLUTION: Bob is making a 40-kilometer boat trip. if he travels at 30 kilometers per hour for the first 10 kilometers, and then at 15 kilometers per hour for the rest of the trip, how many m

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Question 212115: Bob is making a 40-kilometer boat trip. if he travels at 30 kilometers per hour for the first 10 kilometers, and then at 15 kilometers per hour for the rest of the trip, how many minutes more will it take him than if he tarvels the entire trip at 20 kilometers per hour?
Answer by drj(1380) About Me  (Show Source):
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Bob is making a 40-kilometer boat trip. If he travels at 30 kilometers per hour for the first 10 kilometers, and then at 15 kilometers per hour for the rest of the trip, how many minutes more will it take him than if he travels the entire trip at 20 kilometers per hour?

Step 1. Translate following into an equation: He travels at 30 kilometers per hour for the first 10 kilometers. We note that

Distance=Velocity*Time

10+=+30x
x=10%2F30 hours
x=10%2F30%2A60 minutes where 60 minutes = 1 hours
x=20 minutes


where Distance = 10 km, x is the time he travels at 30 kilometers per hours and 30x is the distance traveled.

Step 2. 15 kilometers per hour for the rest of the trip which in this case is 10 kilometers = 40-30.
10=15y
y=2%2F3 hours
y=%282%2F3%29%2A60 minutes
y=40 minutes

Step 3. Add Step 1 and Step 2 for Total Time.

Total time = 20 minutes + 40 minutes = 60 minutes = 1 hour

Step 4. Last part of the problem means he travels 40 km at 20 kilometers per hour.

40+=+20z
z+=+40%2F20 hour
z+=+1%2F2+ hour
+z+=+1%2F2%2860%29 minutes
+z+=+30 minutes

where z is the amount of time for this part of the problem.

Step 5. The amount of time in Step 3 is 60 minutes and amount of time in Step 4 is 30 minutes. So Step 3 is 30 minutes more than Step 4.

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