Problem Solving

Hi All,

We're told that a vehicles travels at a constant speed of 72 kilometers per HOUR. We're asked what that speed is in kilometers per SECOND. This question is really just about 'unit conversions', although at a certain point you can use the 'spread' of the answer choices to your advantage and stop doing 'math.'

1 hour = 60 minutes
1 minute = 60 seconds
1 hour = (60)(60) = 3600 seconds

72 km/3600 seconds

Since 72/720 = .1, we know that 72/3600 is far LOWER than .1
There's only one answer that matches...

Final Answer: A

GMAT assassins aren't born, they're made,
Rich

Here's an easy way to set up UNIT CONVERSIONS - set it up as fractions, so that numerators and denominators of the same unit cancel:





Now there's no confusion about whether to multiply or divide, etc. Now simplify: take a 6 out of each 60, and two 6's out of 72:



We're left with 2 km every 100 sec, or 0.02 km/sec.

The answer is A.

For more on doing unit conversions correctly, see:
https://www.manhattanprep.com/gmat/blog ... ike-a-pro/
https://www.manhattanprep.com/gmat/blog ... our-units/

"Units Control" has a great space-age ring to it, like something you'd shout from the bridge on Star Trek! I like it.

swerve wrote:At a constant speed of 72 kilometers per hour, a vehicle travels how many kilometers per second?

A. 0.02
B. 0.2
C. 0.6
D. 1.2
E. 6.0

Since 1 hour = 3600 seconds, 72 km/hour = 72/3600 = 1/50 = 0.02 km/second.

Answer: A