A popular racetrack is 2.5 miles long. A race is completed in 150 laps. One year, the winners average speed was 161 miles per hour. During cautionary lap runs, the speed was only about 80 miles per hour. If the race had 30 cautionary laps, about how long did it take the winner to complete the race

9514 1404 393

  2:19:45 hours if "average speed" is for all laps

  2:48:03 hours if "average speed" is for full-speed laps only

Step-by-step explanation:

If we assume that the 161 mph average speed is the average over the entire race, then the time is ...

  time = distance/speed

  time = (2.5 mi/lap)(150 laps)/(161 mi/h) = (375 mi)/(161 mi/h) ≈ 2.3292 h

  ≈ 2 h 19 min 45 s

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Additional comment

The meaning of "average speed" in this context is unclear. If we assume the average speed applies only to non-cautionary laps, then the time is ...

  time = distance 1/speed 1 + distance 2/speed 2

  time = (30 laps)(2.5 mi/lap)/(80 mi/h) +(120 laps)(2.5 mi/lap)/(161 mi/h)

  = (75 mi)/(80 mi/h) +(300 mi)/(161 mi/h) ≈ 0.9375 h + 1.8634 h ≈ 2.8009 h

  ≈ 2 h 48 min 3 s

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Hours can be converted to HH:MM:SS by subtracting the integer part and multiplying the fractional part by 60, then repeat. The integer parts in this process are the sexagesimal (base-60) digits of HH:MM:SS from left to right.

fahrenheit

step-by-step explanation:

fahrenheit is more precise than celsius. the ambient temperature on most of the inhabited world ranges from -20 degrees fahrenheit to 110 degrees fahrenheit—a 130-degree range. on the celsius scale, that range is from -28.8 degrees to 43.3 degrees—a 72.1-degree range. this means that you can get a more exact measurement of the air temperature using fahrenheit because it uses almost twice the scale.

1. 3. can also be expressed as (22/7)

2. -4.5

3. 3.6

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