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If Alex drives 80 miles per hour from her house to work and 100 miles 05 Nov 2018, 01:12
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77% (01:40) correct 23% (01:28) wrong based on 148 sessions

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If Alex drives 80 miles per hour from her house to work and 100 miles per hour from work to her house, and drives along the same route both ways, which of the following is the closest approximation of her average speed, in miles per hour, for the round trip?


A. 80.0
B. 88.9
C. 90.0
D. 91.1
E. 100.0
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B
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If Alex drives 80 miles per hour from her house to work and 100 miles 05 Nov 2018, 09:28
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Avg speed when same distance is covered at different speeds = 2ab/(a+b) .where a and b are two speeds

So 2x80x100 / 100+80 = 88.9 mph B

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If Alex drives 80 miles per hour from her house to work and 100 miles 05 Nov 2018, 11:21
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Bunuel
If Alex drives 80 miles per hour from her house to work and 100 miles per hour from work to her house, and drives along the same route both ways, which of the following is the closest approximation of her average speed, in miles per hour, for the round trip?


A. 80.0
B. 88.9
C. 90.0
D. 91.1
E. 100.0

Let's assign a "nice" value to the distance Alex drives each way.
By "nice" I mean a value that works well with 80 mph and 100 mph

So, let's say the distance from home to work = 400 miles

Average speed = (TOTAL distance traveled)/(TOTAL travel time)

TOTAL distance traveled = 400 + 400 = 800 miles

TOTAL travel time = (travel time from home to work) + (travel time from work to home)

travel time = distance/speed
TOTAL travel time = (400/80) + (400/100)
= 5 + 4
= 9 hours

So, AVERAGE speed = 800/9
≈ 88.9

Answer: B

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Brent
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If Alex drives 80 miles per hour from her house to work and 100 miles 06 Nov 2018, 08:23
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Bunuel
If Alex drives 80 miles per hour from her house to work and 100 miles per hour from work to her house, and drives along the same route both ways, which of the following is the closest approximation of her average speed, in miles per hour, for the round trip?


A. 80.0
B. 88.9
C. 90.0
D. 91.1
E. 100.0


average speed = total distance /total time

time 1 = \(t_1\)

time 2 = \(t_2\)

let distance be x

total time = \(t_1\) + \(t_2\) = \(\frac{x}{80} +\frac{x}{100}\)= \(\frac{9x}{400}\)

AVE speed = 800/ 9x/400 = B
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If Alex drives 80 miles per hour from her house to work and 100 miles 07 Nov 2018, 18:58
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Bunuel
If Alex drives 80 miles per hour from her house to work and 100 miles per hour from work to her house, and drives along the same route both ways, which of the following is the closest approximation of her average speed, in miles per hour, for the round trip?


A. 80.0
B. 88.9
C. 90.0
D. 91.1
E. 100.0

We can use the formula of total distance/total time. We can also let the distance each way = 400 and we have:

average = 800/(400/80 + 400/100)

average = 800/(5 + 4)

average = 800/9 ≈ 88.9

Answer: B
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If Alex drives 80 miles per hour from her house to work and 100 miles 03 May 2023, 08:43
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