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Courtney rode her scooter to the library at a rate of 25 mph and then continued to school at a rate of 15 mph. It took her 4 minutes longer to get to the library than it did for her to get to the school from the library. If she traveled a total of 15 miles, how long did it take for her to get to the library? (Hint: Convert either hours to minutes or minutes to hours)

Respuesta :

sqdancefan

Answer:

  24 minutes

Step-by-step explanation:

Let t represent the time in hours it took Courtney to get to the library. Then the time it took to get to school was (t-4/60). The relationship between speed and distance is ...

  speed × time = distance

We can add up the two distances traveled and make sure it totals 15 miles:

  25 × t + 15 × (t-4/60) = 15

  25t + 15t - 1 = 15 . . . . . . . . . eliminate parentheses

  40t = 16 . . . . . . . . . . . . . . . . add 1, collect terms

  16/40 = t = 24/60 . . . . . . . . divide by the coefficient of t, convert to minutes

It took Courtney 24 minutes to get to the library.

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Comment on minutes and hours

A minute is 1/60 of an hour, so 4 minutes is 4/60 = 1/15 of an hour, and 2/5 or 4/10 of an hour is 24/60 hours, or 24 minutes.

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