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Math Expert V
Joined: 02 Sep 2009
Posts: 56371
A car is being driven on a road. Assuming that the car's wheels turn  [#permalink]

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1
3 00:00

Difficulty:   5% (low)

Question Stats: 88% (00:57) correct 12% (00:56) wrong based on 147 sessions

### HideShow timer Statistics Tough and Tricky questions: Geometry.

A car is being driven on a road. Assuming that the car's wheels turn without slipping, how many full 360° rotations does each tire on the car make in 10 minutes?

(1) The car is traveling at 50 miles per hour.
(2) Each tire has a radius of 20 inches.

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Intern  Joined: 12 May 2013
Posts: 27
Concentration: Finance, Economics
GMAT 1: 700 Q49 V36 Re: A car is being driven on a road. Assuming that the car's wheels turn  [#permalink]

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2
Bunuel wrote:

Tough and Tricky questions: Geometry.

A car is being driven on a road. Assuming that the car's wheels turn without slipping, how many full 360° rotations does each tire on the car make in 10 minutes?

(1) The car is traveling at 50 miles per hour.
(2) Each tire has a radius of 20 inches.

(1) The car is traveling at 50 miles per hour.

We do not know the circumference of the each tire!

They could be small as wolkswagen bubble tires (many rotations) or large as monstertruck tires (fewer rotations)

NOT SUFFICIENT

(2) Each tire has a radius of 20 inches.

We do not know the speed of the car!

Standing still = 0 rotations
The car is actually traveling = more than 0 rotations

NOT SUFFICIENT

(1) + (2)

Distance traveled = $$50 * \frac{1}{6} = \frac{50}{6} miles$$
Circumference of the each tire = $$20*2*pi = 40*pi inches$$

Rotations = $$\frac{50}{6} miles / 40*pi inches$$ (You don't have to do the calculations!)

SUFFICIENT

OA is C

Sorry for the messy expressions, $$pi inches$$ = 3,14 inches _________________
Feel free to message if you have any questions :D
Director  G
Joined: 26 Oct 2016
Posts: 626
Location: United States
Schools: HBS '19
GMAT 1: 770 Q51 V44 GPA: 4
WE: Education (Education)
Re: A car is being driven on a road. Assuming that the car's wheels turn  [#permalink]

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Consider the RT = D formula (rate × time = distance).

D, the total distance traveled by the car, will be equal to C, the circumference of each tire, times N, the number of 360° rotations made by each tire. Thus, we can rewrite our formula as RT = C*N.

The question is asking us how many 360° rotations each tire makes in 10 minutes. In other words, it is asking us for the value of N when T = 10. We can rewrite our equation thus:

R(10) = C*N

N = R(10)/C

Clearly, in order to answer the question “what is N” we need to know both R and C.

(1) INSUFFICIENT: This only gives us R, the speed of the car.

(2) INSUFFICIENT: This gives us the radius of the tire, which enables us to find C, the circumference of the tire. Knowing C is not, however, sufficient to figure out N.

(1) AND (2) SUFFICIENT: Now that we know both R and C, we can figure out what N is from the equation N = R(10)/C.
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Anaira Mitch
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Re: A car is being driven on a road. Assuming that the car's wheels turn  [#permalink]

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_________________ Re: A car is being driven on a road. Assuming that the car's wheels turn   [#permalink] 27 Jun 2019, 18:44
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