Sprouts | Ball-Parking: Get Better Grades Through Elimination @sprouts | Uploaded April 2017 | Updated October 2024, 1 hour ago.
Learn how to improve your grades using the ballparking technique, in this 4:55 minute long video lesson.
Use ballparking when you have no time to solve the complete problem.

Join us at patreon.com/sprouts and check out the GMAT training app from The Economist at https://gmat.economist.com. We took our math example from there and it's a great tool to learn for the GMAT and train your thinking.

Script:

Ball-parking is a technique that helps us to solve problems quickly. Instead of trying to get the perfect result, we make a fast, intelligent guess. Just like in baseball. To score, we don't need to hit the ball perfectly. Often we just need to keep it inside the ballpark. The technique is useful in conversations and is essential to passing certain tests. To watch this video most effectively, grab a pen and paper, and try solving the following two problems as we present them. Just pause whenever you see this sign.

Let’s start easy! What do you think is the most popular food in the world? Could it be Italian, Japanese, American fast food, or something else? As it is impossible to get an exact answer, let’s look at what we may already know. In Italy, there are around 50 million people, in Japan about 100 million and in North America about 500 million. But in China or in India there live over a billion people. Now we can use the process of elimination and make a ballpark estimate that Chinese and Indian food is probably the most popular.

Now let's try something a little harder. Imagine that you are doing a complicated math test for something like the GMAT exam. Then you might just 2 minutes to solve complex problems in your head. Maybe something like the square root of 5 times the square root of 24, plus 5 divided by, 5 plus 2 times the square root of 6. Then you're given five multiple-choice answers: A, B, C, D or E. If we would try to solve it, we would probably run out of time. Ball-parking is now the only option. You can try it on your own or do it with us.

Look at the equation. Let's look at the first part, the square root of 24. Since the square root of 24 is difficult to calculate in your head, think of a close enough number to the square root of 24 that would be easier for you. The square root of 25 comes to mind. To which the answer is 5. Let’s now write down the new simpler equation and then again even simpler. Now, what about the fraction? It looks hard, but let's try! Even if we don't know what 5 plus 2 times the square root of 6 is, we do know that it's more than 5. So let's write it again and just call the denominator [6.1] “more than 5”. And because 5 divided by anything larger than 5 must be smaller than 1, we can just write “25 plus less than 1 or the square root of 25. And that equals approximately 5. Lets now look at the options we were given.

Let's look at the equation and each possible choice.
A is clear and doesn't look bad.
B is 5 plus 2 times the square root of 6 which is something like 7 or more. That doesn't look right.
C is the square root of something that comes out to be 3 or less. That's too small.
What about D? The square root of 120. We don't know that, but we do know that the square root of 100 is 10. Let's just write 10 or more. That looks too high.
Last, there is E. 5 divided by 2 times the square root of 6. Now for 2 times the square root of 6 let's just write “more than 2”. And 5 divided by something that's more than 2 also looks too small.

Now we use the process of elimination and cross out all the wrong answers to see what's left.
A, it is.

Now it's your turn. Try ball-parking the number of views that you think this video will have by the end of this year and win your favorite Sprouts gift on Patreon.com/Sprouts We will count all entries submitted by August 31st and announce the winner on the 1st of January. To join, just leave your ballpark figure in the comments below. And if you want, tell us how you did it. Those of you who post later than August 31st will enter next year's round of Sprouts Ballpark Awards. Good luck!

SOURCES
Visit gmat.economist.com