While getting ready for the GMAT, you may need to devote some energy to re-learning math concepts for the Quantitative Reasoning and Integrated Reasoning sections. But no matter how much of a “math person” you are, one skill you MUST be comfortable with is estimation. A good GMAT score requires you to estimate confidently.

Knowing when to use estimation on the GMAT

When you estimate, you use an approximate value that is near the actual value but easier to work with. In the Quantitative Reasoning section—where you do not have a calculator—estimate whenever possible instead of taking the time to perform detailed calculations. In Integrated Reasoning, where you do have a calculator but don’t have any time to spare, estimate instead of using the calculator. The key to smart estimating is knowing when to use it.

There are a number of clues to help you determine whether estimating is appropriate:

• If the question uses the word approximately, estimating is almost always your best bet.
• If the answer choices are widely spaced, estimating is usually a good idea.
• If the answer choices have 0 as the units digit, estimating is usually a smart option.

Estimating to solve Quantitative Reasoning problems

Some questions have all three of the above clues, while others may only have one or two. Here’s a sample problem that illustrates all three:

Jack wants to make a roundtrip flight to visit his parents. He has a choice of 37 different flights to his destination and 42 different return flights. Assuming there are no restrictions on which flights can be taken, approximately how many different combinations of flights are available to Jack for his trip?

• 500
• 900
• 1200
• 1600
• 2000

Because the question asks for an approximate number, estimation is a good option. There are significant gaps between the answer choices, and they all end with 0. This means rounding both 37 and 42 to 40 is allowable and points you to the answer with little effort: There are approximately 1,600 combinations available to Jack. Multiplying the actual values would clearly be unnecessary here.

Be careful with approximate quantities

One thing to keep in mind when rounding: If you round multiple values in the same direction, you may skew the result too far. If, for example, the values in the question above had been 37 and 47, the rules for rounding would have you round them both up. Be aware, in that case, that your approximate value will be higher than the actual value.

Because the GMAT is a critical thinking test, remember that using logic and strategy are just as important as using math skills. Estimate whenever possible; the GMAT will reward you for it.

Want to get more Quantitative Reasoning practice before Test Day? Sign up for a free GMAT practice test and review to see how you perform.

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