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Solve Just About ANY Math Problem with this Trick

+12 votes
asked Nov 12, 2016 in Ask Whizkid by whizkid (65,230 points)
edited Nov 12, 2016 by whizkid

Today's advice will teach you what I consider the most powerful math trick in the world. You can solve almost anything with it and I can teach it to you very easily. If you master it you will have a big advantage over other students and get many more problems correct on tests.


It is all about units and the method is called Dimensional Analysis. The key is to understand that units cancel if divided by themselves.

meter / meter = nothing, since you are cancelling out the units.

kg / ounce X ounce /kg = nothing

You just draw lines through any units that are divided by the same unit. However, leave any numbers in front of it alone.

We can now apply it and solve what would otherwise be a very tough problem very simply.

Example: Convert 25 kg to ounces

Step 1. Put down whatever you know.

25 kg 

We also know 1 ounce = 28 g and 1000 g = 1 kg

Just arrange what you know so what is left are the final units and your answer will "magically" appear.

25 kg X 1000 g / 1 kg 

Don't do any math until you get the final units you want, which are ounces in this example. We now just have grams (g), so continue the unit cancelling.

25 kg X 1000 g / 1 kg  X  1 ounce / 28 g

We are now done! The answer is 25 X 1000 / 28 = 892.9 ounces

Another example. How many seconds are in 4 hours?

You know 60 s in a minute, 60 min in an hour

4 hours X 60 min / 1 hour X 60 s / 1 min = 4 X 60 X 60 = 14,400 seconds

It takes all the guesswork out of math and makes very tough problems routine. You won't ever make the mistake of not knowing which number goes on the top during a conversion step, since only one spot will make things cancel. People will think your are a "genius" at math with this system. I was near the bottom in my math class before learning it and quickly got top scores in the most advanced level at school after learning it.

Truly one of the greatest math techniques in the world. It works because the things you are multiplying, like 1 ounce / 28 g, are all equal to '1' because they are the same thing on the numerator and denominator.

commented Nov 13, 2016 by happyL (430 points)
reshown Nov 14, 2016 by happyL
i love that so helpful i tried it on my test
commented Nov 13, 2016 by whizkid (65,230 points)
Glad you like it! You don't need to think when using it, just follow the simple rules. If you have any questions about it, please let me know.
commented Nov 14, 2016 by rae (86,770 points)
I thought you were talking about actual math, not whatever the heck THAT was. Conversions? That's not even math.
commented Nov 14, 2016 by whizkid (65,230 points)
edited Nov 14, 2016 by whizkid
All math is nothing more than converting one thing to another. It might be converting a very complex equation to a number, or to simplified form. People who are good at math focus on that part and it just helps them to became even better.

You can use the same method to solve algebra equations. Even word problems are usually nothing more than conversion questions in words.

It may not be for everyone. If I can help just one person do better in school it will have been worth my time.

You can even solve hard physics problem without knowing the physics equations. Example. How much energy does it take to throw a 2 kg rock 10 meters straight up?

I know energy is Joules, which is kg m^2/s^2 in basic SI units. All I need to do is keep cancelling until I get "kg m^2/s^2". I know gravity is 9.8 m/s^2

2 kg x 10 m x 9.8 (m/s^2) = 2.04 kg m^2 s^2 = 2.04 Joules, which are the correct units, so I solved it without even knowing the formula! Impressed yet?

1 Answer

0 votes
answered Nov 14, 2016 by happyL (430 points)
not true it helped a lot  i think you are wrong cindystrong rae

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