Problem Solving

The rear wheels of a car crossed a certain line 0.5 second after the front wheels crossed the same line. If the centers of the front and rear wheels are 20 feet apart and the car traveled in a straight line at a constant speed, which of the following gives the speed of the car in miles per hour? (5,280 feet = 1 mile)

A) (20/5,280)(60^2/0.5)
B)(20/5,280)(60/0.5)
C)(20/5,280)(0.5/60^2)
D)(20*5,280)/(60^2)(0.5)
E)(20)*(5,280)/(60)(0.5)


The answer is A.


Please explain.

Thank u.

for the rear wheels to pass the object after the front wheels have passed them, the distance rear wheel has to cover = distance from the rim of the front wheel to the end rim of the rear wheel. So in effect it is the distance between the centres of the tow wheels. this is 20 ft or (20/5280) miles.
Time taken to cover pass the object = 0.5 secs or (0.5/3600) hours or (0.5/60^2) hours.

So the speed would be (20/5280)/(0.5/60^2) = (20/5280)(60^2/0.5) which is option A.

hakyology wrote:The rear wheels of a car crossed a certain line 0.5 second after the front wheels crossed the same line. If the centers of the front and rear wheels are 20 feet apart and the car traveled in a straight line at a constant speed, which of the following gives the speed of the car in miles per hour? (5,280 feet = 1 mile)

A) (20/5,280)(60^2/0.5)
B)(20/5,280)(60/0.5)
C)(20/5,280)(0.5/60^2)
D)(20*5,280)/(60^2)(0.5)
E)(20)*(5,280)/(60)(0.5)


The answer is A.


Please explain.

Thank u.

You can easily pick the answer from the choices.

We are converting ft to mile therefore we have to divide. You can eliminate D and E.
You can also eliminate B because it is converting only in minutes not in hours.

Answer C is trap answer.

We know Speed= Distance/Time

(20/5280) / (0.5/60^2) => (20/5280) (60^2/0.5)

Hence A is the correct answer.

I can't figure how they came up with the (60^2/0.5)


dsk you said:

"So the speed would be (20/5280)/(0.5/60^2) = (20/5280)(60^2/0.5) which is option A." which is the same as answer C = answer A


could someone explain, why it is (60^2/0.5) and not (0.5/60^2)?

thank you!

Carol wrote:I can't figure how they came up with the (60^2/0.5)


dsk you said:

"So the speed would be (20/5280)/(0.5/60^2) = (20/5280)(60^2/0.5) which is option A." which is the same as answer C = answer A


could someone explain, why it is (60^2/0.5) and not (0.5/60^2)?

thank you!

answer C does not have a fraction sign

(20/5280)/(0.5/60^2) = (20/5280)(60^2/0.5)

Hope this helps

that was it

thx! parallel_chase

Thank you so much, parallel_chase