A car is being driven on a road. Assuming that the car's wheels turn

VeritasKarishma plz solve this

Question: Number of revolutions in 10 mins = ?



Statement 1: Speed = 50 miles/hour
Speed is known but the radius of wheel is unknown hence

NOT SUFFICIENT

Statement 2: Radius = 20
Radius of wheel is known but the Speed is unknown hence

NOT SUFFICIENT

COmbining the statements

Radius = 20
Speed = 50 miles/hour

SUFFICIENT

Answer: Option C
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Sentence 1 - Car speed 50 miles per hour.....No information of wheel... Not sufficient
Sentence 2 - Each tire has a radius of 20 inches...No information car speed....Not sufficient

Both Sentences together
We get disatance of car travelling as well distance per rotation.
Sufficient

Ans C

How will you calculate the number rotations made in 10 mins? That will depend on the distance covered in 10 mins and the circumference of the wheel.

No of rotations = Distance covered/Circumference of the wheel

Say a distance of 2000 m is covered in 10 mins and the circumference of the wheel is 1 m. Then number of rotations made by the wheel = 2000/1 = 2000 rotations.

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

Since you have the speed of the car, you can find the distance covered in 10 mins as distance = speed * time.
But you do not know the circumference of the wheel yet.
Not sufficient.

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

With radius you can find the circumference but you do not know the distance covered. Not sufficient.

Using both, you can find the number of rotations.
Sufficient.

Answer (C)

Do not try to actually calculate in such questions. You will waste precious time. They have given quantities in different units and the numbers don't round up well.

KarishmaB
Hi there
I am wondering that how two statements combined are sufficient
because statement 1 only tell us that 【 The car is traveling at 50 miles per hour】
but it did not say 【constant speed】
which means that it can travel either 49 miles per 10 mins or 1 miles per 10 mins
Is that an official problem? not critical enough
or something wrong with my thinking process

Plz sheild some lights, appreciate that

A car is travelling at 50 mph means that this is the speed of the car (note the use of simple present - it wouldn't make sense if the car were not maintaining this speed). So the speedometer is showing 50. There is no ambiguity here. This is a constant speed that the car is maintaining.
If we were given that a car covered 50 miles in an hour, then yes, we wouldn't know what the actual speed of the car was during that one hour. All we would know is that the average speed was 50 mph.
But in our question above, we are simply given the constant speed of the car. An actual GMAT question might mention the word "constant" for clarity but there is no ambiguity as given either.