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We are GMAT Mentors, a non-profit focused on facilitating the free exchange of GMAT knowledge, support, and advice through one-on-one mentoring.
Since launching our service, we have gotten a lot of positive feedback from both mentees and mentors! We have had requests to start a tip/principle of the week, so we have decided to do just that. Each week we post a tip, trick, or principle focusing in either Verbal or Quant. You may already know some of these, but hopefully you will see something new! A full collection of all of our tips of the week can be found through our website (gmatmentors.com)
To set the stage on why estimation is an essential component of quant questions, it is important to understand that the GMAT will never expect you to do complex calculations in your head. If you ever find yourself feeling like you need to do calculations with very large numbers, take a second and think about how you can use estimation to solve the problem.
In general, rounding to easily manipulated numbers is the key way to use estimation. If you see 9.5^2 , you should immediately realize, this is between 81 and 100, but should not immediately care what the exact number is. How exact you need to understand any number will of course vary by question, but the general use of estimation is ALWAYS useful for quick solutions.
One good example where estimation is essential is shown below:
Question:
The product of all prime numbers less than 20 is closest to which of the following powers of 10?
Answer choices:
As you can imagine, the first step to answer this question is to list all of the prime numbers:
2, 3, 5, 7, 11, 13, 17, 19
This is where the question gets difficult. You could multiple all of the numbers exactly as they are to see the result; however, this would take a lot of calculations and time. The GMAT would never expect you to multiple all of these numbers together to get the exact result, this just takes too much time.
So instead of multiplying each number as they are, we should look for combinations of numbers that are close to 10. Lets use estimation to get combinations of 10:
Now 13 and 17 are slight stretches in this context, however the fact that we overestimate 17 and underestimated 13 makes this feel okay, and ultimately we are looking for orders of magnitude of 10, which this estimation does not violate.
Okay, so now we have 10^6 * 2^3. 2^3 is equal to 8, which can be estimated to equal 10. Therefore, 10^7 is the final answer!
Using estimation you can answer this question in less than a minute and feel confident in your answer without taking a ton of time to do detailed calculations.
Thanks for reading and as always - If you would like to become a mentee and receive personalized support or become a mentor and help others, please check out our website or email us!
Email: [email protected]
Website: https://www.gmatmentors.com
Since launching our service, we have gotten a lot of positive feedback from both mentees and mentors! We have had requests to start a tip/principle of the week, so we have decided to do just that. Each week we post a tip, trick, or principle focusing in either Verbal or Quant. You may already know some of these, but hopefully you will see something new! A full collection of all of our tips of the week can be found through our website (gmatmentors.com)
To set the stage on why estimation is an essential component of quant questions, it is important to understand that the GMAT will never expect you to do complex calculations in your head. If you ever find yourself feeling like you need to do calculations with very large numbers, take a second and think about how you can use estimation to solve the problem.
In general, rounding to easily manipulated numbers is the key way to use estimation. If you see 9.5^2 , you should immediately realize, this is between 81 and 100, but should not immediately care what the exact number is. How exact you need to understand any number will of course vary by question, but the general use of estimation is ALWAYS useful for quick solutions.
One good example where estimation is essential is shown below:
Question:
The product of all prime numbers less than 20 is closest to which of the following powers of 10?
Answer choices:
- 10^9
10^8
10^7
10^6
10^5
As you can imagine, the first step to answer this question is to list all of the prime numbers:
2, 3, 5, 7, 11, 13, 17, 19
This is where the question gets difficult. You could multiple all of the numbers exactly as they are to see the result; however, this would take a lot of calculations and time. The GMAT would never expect you to multiple all of these numbers together to get the exact result, this just takes too much time.
So instead of multiplying each number as they are, we should look for combinations of numbers that are close to 10. Lets use estimation to get combinations of 10:
- 2*5 = 10 (no estimation needed)
3*7 ~=2*10
11~=10
13~=10
17 ~=2*10
19~=2*10
Now 13 and 17 are slight stretches in this context, however the fact that we overestimate 17 and underestimated 13 makes this feel okay, and ultimately we are looking for orders of magnitude of 10, which this estimation does not violate.
Okay, so now we have 10^6 * 2^3. 2^3 is equal to 8, which can be estimated to equal 10. Therefore, 10^7 is the final answer!
Using estimation you can answer this question in less than a minute and feel confident in your answer without taking a ton of time to do detailed calculations.
Thanks for reading and as always - If you would like to become a mentee and receive personalized support or become a mentor and help others, please check out our website or email us!
Email: [email protected]
Website: https://www.gmatmentors.com
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