Part (a)
Answer: 0.2
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Work Shown
It costs $15 to rent a bike for 3 hours. We can write the following ratio below
15 dollars : 3 hours
To represent the connection of the two concepts (dollars connecting with hours)
We want the "15 dollars" to turn into "1 dollar". This is because the phrasing "per dollar" really means "per 1 dollar".
Divide both sides of the ratio by 15 to achieve this goal.
15 dollars : 3 hours
15/15 dollars : 3/15 hours
1 dollar : 1/5 hours
1 dollar : 0.2 hours
0.2 hours : 1 dollar
So we get 0.2 hours per dollar.
As a side note, 0.2 hours = 0.2*60 = 12 minutes.
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Part (b)
Answer: 3.38
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Work Shown
27 pages : 8 minutes
27/8 pages : 8/8 minutes
3.375 pages : 1 minute
3.38 pages : 1 minute
I'm dividing both parts of the original ratio by 8 to turn "8 minutes" into "1 minute" (due to the phrasing "per minute"). Don't forget to round to 2 decimal places.