# How to Subtract Faster Than Your Teacher

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Okay, here is a little secret...

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When you subtract a BIG number FROM a SMALL number...

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It is the same as subtracting the SMALL number FROM the BIG number and making it NEGATIVE. (And that is much easier to subtract!)

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So, now that you know that secret, you can SUBTRACT FASTER THAN YOUR TEACHER!...

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What is 274 - 197?

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We can do this one column at a time. 200-100 = 100 (No flipping required!) Save the 100 in your head.

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70 - 90 is the same as 90-70, which is 20, but it is NEGATIVE. (-20) MINUS 20. Save it upstairs.

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And 4 - 7 is the same as 7 - 4... but it's negative! (-3) MINUS 3. Got it?

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So that's 100 - 20 - 3 which is 80 - 3 which is 77!

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Too easy huh?

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If I lost you, go through it again. hehe

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UH OH! Another one? ! Let's see here... (genius inquisitive look)...

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100 - 800 is the same as 800 - 100, but it is negative. So that is -700. CHECK!

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40 - 80 is the same as 80 - 40, but it is negtaive. -40. DOUBLE CHECK!

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And 3 - 9 is the same as 9 - 3, but it is negative. -6. WE GOT THIS!

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So that is -700 - 40 - 6. UH... That's a little complicated T.D. What ever shall I do!!!?

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That means it is time for another SECRET! If all of those numbers were either POSITIVE or NEGATIVE then we handle them better.

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The -700 is a NEGATIVE. When we put that -40 in front of it, we are actually subtracting a POSITIVE 40. And it's the same with the 6. We are subtracting a POSITIVE 6.

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So we need to change ALL the numbers to either negative, or all of them to positive. I am going to change the 40 and the 6.

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But how?

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Well, when you SUBTRACT a POSITIVE number it is the same as ADDING a NEGATIVE number. So the MINUS 40 becomes PLUS NEGATIVE 40. Same for the 6.

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So now it is -700 + -40 + -6, AH! EASIER! Just add them like you would positive numbers but remember that the answer will be NEGATIVE. -746!

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We are ADDING a POSITIVE number, but that -700 is still negative. So we need another trick (Which is just like the last trick.)

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It is just like SUBTRACTING a NEGATIVE. -700 - -40 - -6. That is like 700-40-6 which is like 660 - 6 BUT IT'S NEGATIVE. -654

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What about this? Well we know what we need to do. We need to make them all negative or positive.

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-700 + -40 - -6. That is just like 700+40-6 BUT IT IS NEGATIVE. -734

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Let's clear this up a little bit...

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IF you have a PLUS sign it is like SUBTRACTING A NEGATIVE, which makes it MORE POSITVE.

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And when you have a MINUS sign it is like ADDING A NEGATIVE, which makes it MORE NEGATIVE.

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One more!

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Now I can act like a genius and quickly say ''8,6,4,2 NEGATIVE" (Switching them in my head). But let's go through it.

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1,000-9,000 is -8000

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200-800 is -600

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30-70 is -40

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4-6 = -2

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Get ready to flip em! PLUS A NEGATIVE.

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This is like 8,000+600+40+2 BUT ITS NEGATIVE. -8642!

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TA DA!

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THE MASTER CHALLENGE!!!!

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174,367 - 719,718? Anyone?

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Well first I am going to flip it (It seems it's much easier if the first column is normal). And I am going to stick that minus sign off to the side and ignore it for a while.

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Don't worry, I'll bring it back later.

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700,000 - 100,000 = 600,000

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Next group. 10,000-70,000 = -60,000

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And: 9,000 - 4,000 = 5,000 (positive 5,000 that is)

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700 - 300 = 400

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10 - 60 = -50

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And 8 - 7 = 1

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That's 600,000 - 60,000 + 5,000 + 400 - 50 + 1

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WAIT! Don't start flipping! I have another trick (one you wish I told you at first).

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This is how you handle zeros. Line up the biggest numbers and get rid of all the zeros they have in common. They have 4 zeros in common. (60,000 only has 4 zeros).

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Now for the smaller numbers. 400 - 50 = 350 (Do it whichever way is easier to do in your head) + 1 = 351. + 5,000 = 5,351

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You could have also done the 0 TRICK on the 400 and the 50

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Now add that to the 540,000. 545,351!!!!

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NEGATIVE!!

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Told you I'd add it back

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