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Danny drove his old car 100 kilometers, from his home to a friend. To

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Bunuel
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Danny drove his old car 100 kilometers, from his home to a friend. To [#permalink] Danny drove his old car 100 kilometers, from his home to a friend. To   01 Jun 2021, 07:45
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Danny drove his old car 100 kilometers, from his home to a friend. To prevent the engine from overheating, he stopped his car for 10 minutes every time he completed 40 kilometers of continuous driving. When the car was moving, Danny drove it at an average speed of 60 kilometers per hour. What was Danny's average speed on that trip?

A. 37.5 kilometers per hour
B. 48 kilometers per hour
C. 50 kilometers per hour
D. 75 kilometers per hour
E. 100 kilometers per hour
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C
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aniruddhawarang29
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Danny drove his old car 100 kilometers, from his home to a friend. To [#permalink] Danny drove his old car 100 kilometers, from his home to a friend. To   01 Jun 2021, 08:50
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Bunuel wrote:
Danny drove his old car 100 kilometers, from his home to a friend. To prevent the engine from overheating, he stopped his car for 10 minutes every time he completed 40 kilometers of continuous driving. When the car was moving, Danny drove it at an average speed of 60 kilometers per hour. What was Danny's average speed on that trip?

A. 37.5 kilometers per hour
B. 48 kilometers per hour
C. 50 kilometers per hour
D. 75 kilometers per hour
E. 100 kilometers per hour



Let's imagine the following diagram :


H-------------|10min|-------------|10 min|----------F
<--40km--> <--40km--> <-20km->

Avg speed = \(\frac{total distance}{total time}\)

We know total distance - 100.

Now to calc total time we need to calc individual times of each zones and also add the 2 x 10 min breaks he took into the sum.

t1 = 40/60 = 2/3
t2 = 40/60 = 2/3
t3 = 20/60 = 1/3

and Break 2 times = 2*(10/60) = 1/3


Hence, Avg speed = \(\frac{100}{(6/3)}\)
Ans = 50.
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Scuven
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Re: Danny drove his old car 100 kilometers, from his home to a friend. To [#permalink] Danny drove his old car 100 kilometers, from his home to a friend. To   02 Jun 2021, 06:37
you know that car moved at 60 km/h and that the space it travelled was 100 km
You also know that he stopped for 10 minutes (10/60 hours) every 40 km.
Thus he stopped 2 times in 100 km for a total time of ( 2* 1/6) =2/6=1/3

Without the stoppages you can calculate that the time he would travelled would have been (t=s/v) thus 100/60=5/3 hours

With stoppages you know he stopped for a total of 1/3 hours

Thus the total travel lasted for 5/3 + 1/3 = 6/3 =2 hours

And the average speed was v(s/time with pauses included) = 100/ 2=50 thus C
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Re: Danny drove his old car 100 kilometers, from his home to a friend. To [#permalink] Danny drove his old car 100 kilometers, from his home to a friend. To   25 Feb 2024, 01:33
Why we r including stopage time with driving time here ?

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Re: Danny drove his old car 100 kilometers, from his home to a friend. To [#permalink] Danny drove his old car 100 kilometers, from his home to a friend. To   25 Feb 2024, 07:53
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Rikhraj1 wrote:
Danny drove his old car 100 kilometers, from his home to a friend. To prevent the engine from overheating, he stopped his car for 10 minutes every time he completed 40 kilometers of continuous driving. When the car was moving, Danny drove it at an average speed of 60 kilometers per hour. What was Danny's average speed on that trip?

A. 37.5 kilometers per hour
B. 48 kilometers per hour
C. 50 kilometers per hour
D. 75 kilometers per hour
E. 100 kilometers per hour


Why we r including stopage time with driving time here ?­


The average speed equals the total distance divided by the total time, and since the total time includes the time for the stops, the stops should be included in the calculation.
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Re: Danny drove his old car 100 kilometers, from his home to a friend. To [#permalink]
25 Feb 2024, 07:53
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