Here’s How to do GMAT Unit Conversions Like a Pro
Sometimes the whole point of a specific GMAT problem is to convert between miles and kilometers, or meters and centimeters. In other problems, you’ll need to do a unit conversion as part of a longer solution. It’s easy to mess up unit conversions, and the GMAT writers know this — they include them on the test in order to test your level of organization and your ability to double-check your work. Here’s how to add fast unit conversions to your repertoire of skills.
- Write the units down
The easiest mistake to make is simply forgetting what units you’re working with. If the problem asks for a number of cents, but you calculate a number of dollars, you’ll be off by a factor of 100 even if you do all of the math correctly. If there’s any chance that units will come into play in a problem, write them out at every step.
- Treat units like variables
Units can be multiplied, divided, and canceled out, exactly like variables. (Remember that ‘per’ always translates to division.) Suppose you’re converting 1400 crowns to rupees, and you know that the exchange rate is 0.4 crowns per rupee. Do you multiply 1400 by 0.4, or do you divide? Check by trying to cancel out the units:
Wrong:
Right:
Since division causes the units to correctly simplify to rupees, division is correct. Think about which units will need to cancel, and arrange them so that they do.
- One step at a time
With complex unit conversions, don’t skip steps. Convert a single unit at a time. In this example, we’ll convert 15 meters per second to kilometers per hour, by first converting seconds to minutes.
All that’s left is to do the arithmetic, by calculating (15 x 60 x 60)/1000. The result is 54 kilometers per hour.
- Sanity check
Do a basic sanity check each time you finish a unit conversion using familiar units. If you’re converting two hundred dollars to cents, should the result be greater than 200 or less than 200? If you’re converting 45 seconds to hours, should the result be greater than 45 or less than 45? It’s easy to mix up multiplication and division, and quickly checking to make sure your result is sensible can help you avoid this.
- Practice with Google
Type “15 meters per second in kilometers per hour” into a Google search box. Google Calculator automatically handles many unit conversions, including complex ones. That means that you can use it to drill this skill after reading this article! Make up a few complex unit conversions and simplify them on paper, exactly as you would if you saw them on the GMAT. Then, use Google to check your answers.
Half an hour of work, right now, will make you much quicker and more confident at unit conversions. While they don’t appear in every Quant problem, the GMAT test writers love to throw them in at the end of a tricky problem, in the hopes that unprepared test takers will make an easy mistake. Make them part of your GMAT toolkit, and outsmart the test! 📝
Chelsey Cooley is a Manhattan Prep instructor based in Seattle, Washington. Chelsey always followed her heart when it came to her education. Luckily, her heart led her straight to the perfect background for GMAT and GRE teaching: she has undergraduate degrees in mathematics and history, a master’s degree in linguistics, a 790 on the GMAT, and a perfect 170/170 on the GRE. Check out Chelsey’s upcoming GMAT prep offerings here.