Cool Maths Trick

[e1ghtSpace]

Here's a cool thing I found while I was bored in maths class. Here it is:
(you can change the numbers around and it still works)

2x5=10     This is what we will base our calculations off
We will also use 7 just cause.
-----------------
7x5=35
7/2=3.5

We used the 5 and the 2 and if we multiply or divide the answers by the product of the two numbers, we reach the other equation's answer.

7x5=35 / 10 = 3.5
7/2=3.5 x 10 =35

Weird, huh?

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So of you wanted to work out 13 x 25       (Because multiplying 100 is easy)
you could use this to your advantage.

25x4=100        Note: The 4 could be any number but I chose it because 4 x 25 = 100 and it's easy to multiply by 100.

13/4=3.25

3.25 x 100 = 325

So does 13 x 25 = 325?
Yes! So this thing (I don't know what to call it) works!

Comment on what you think.

[Bitcoinexp]

So you mean to say that:
Since, 2 x 5 = 10
Therefore, X x 2 = X x 10/5 ? (big X is unknown, small x is multiply)
If you look carefully at the first equation, you can see the connection
I noticed it a couple of years back, when i started to learn multiplication and division
Sweet ol' times...
I didn't know what it meant back then, but now i realized that i had actually discovered something called "The fraction".

[Billbags]

                  D
60  ------------------------
       Speed x Time


We call this "60 D street" when navigating at sea.  (Distance Speed Time) we use any two we know to get the third we need.
Time is entered in minutes, speed in knots and distance in nautical miles.
The use of "60" ensures that time is calculated in minutes rather than in hours and tenths of an hour.

To find distance, if speed and time (or duration) are known:

D = (S x T) ÷ 60

To find time, if distance and speed are known:

T = (60 x D) ÷ S

To find speed, if distance and time are known:

S = (60 x D) ÷ T


Your math is very similar to this in many ways if you look closely.

[e1ghtSpace]

So you mean to say that:
Since, 2 x 5 = 10
Therefore, X x 2 = X x 10/5 ? (big X is unknown, small x is multiply)
If you look carefully at the first equation, you can see the connection
I noticed it a couple of years back, when i started to learn multiplication and division
Sweet ol' times...
I didn't know what it meant back then, but now i realized that i had actually discovered something called "The fraction".

Oh yeah. It's so simple. Didn't even notice. Thanks for pointing that out.
Ooh, you discovered this: http://en.m.wikipedia.org/wiki/Fraction_(religion) jks.

[Gleb Gamow]

So of you wanted to work out 13 x 25       (Because multiplying 100 is easy)
you could use this to your advantage.

25x4=100        Note: The 4 could be any number but I chose it because 4 x 25 = 100 and it's easy to multiply by 100.

13/4=3.25

3.25 x 100 = 325

So does 13 x 25 = 325?


25 x 13 = X   Note: The 13 could be any number but I chose it because...

13/13 = 1

1 x X = X

So does 13 x 25 = X

Yes it does.

Q.E.D.

25 x 2 = 50   Note: The 2 could be any number but I chose it because...

13/2 = 6.50

6.50 x 50 = 325


13/x X 25x = ?

(13 X 25) X x/x = ?

(13 X 25) X 1 = ?