Welcome to the SUPER BRAIN TABLE *Note:
this table is intended only for those who want SUPER math brain
power. *HERE is a deck of flash cards to help you learn these POWER facts. *HERE is an ELECTRONIC set of flashcards. Just set it to fit your practice needs and play till you are at 100%. *When you think you know them
all, try the THE
MENTAL MATH POWER ZONE! guaranteed
to make you SMARTER. Actually
this table is not really as bad as it looks at first. The
bottom half contains repeats for each pair:
Take a look at the triangular shaded area below to see what we mean.
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MULTIPLYING
BY A SUM: Let's say you want to multiply 27 x 6 easily. You can break the 27 up into 20 and 7. You do this because it is easy to multiply by 20 and it is easy to multiply by 7. You use a "divide and conquer" approach to the problem. Take something a bit difficult and break it down into two easier parts. Technically this is called the DISTRIBUTIVE PROPERTY for MULTIPLICATION. Okay so now we have (20+7)6. We will multiply the 6 times both the parts of 27 and then add the results (these results are known as "partial products"). 20x6=120 and 7x6=42. So our answer is 120 + 42 = 162. The idea is for this to be done in your head. It will even work for larger numbers, however if they get too large you might need to jot down some of the "partial products". EX: 325 x 3
= (300 + 20 + 5)3 = This also works for two digit numbers. Let's try one
from the table above, 17 x 13. Now those four partial products might be hard to keep in your head all at once, but we've noticed that if you think about it like this: .....(10 + 7) x...(10
+ 3) both the 3 and the 7 get multiplied by 10 to make 30 + 70 =100 and finally you multiply the 3 times the 7= 21 so it is just 100 plus 100 which is 200 plus 21 more = 210 keep a running total in your head; you'll be amazed how fast you will get with practice
MULTIPLYING BY A DIFFERENCE: (this is known as the Distributive Property of Multiplication over Subtraction) This trick is great for multiplying by numbers ending in nine like 9, 19, 99, 999, etc. The reason people HATE to multiply by nine is that you always end up carrying a part of the answer into the next left column. That way it is easy to make mental mistakes, even if you are using a pencil! So here we go: since 9, 19, 99, 999 are a pain, turn them into 10, 20, 100, or 1000 respectively, because it's easier to multiply by a number ending in zero than one ending in 9. What....you say we can't just change 9 into 10! Well technically you are correct.....so how about 9 = (10-1). Now that is undeniably true, and it is easy to multiply by 10 and by 1. This is what it looks like: EX: 13 x 9........is
the same as 13 x (10 - 1). 130 - 13 = 117 EX: 14 x 19......think of this as 14 x (20 -1) 280 - 14 = 266 The more you
do the faster you will get.
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