Trick No. 6 – Rapidly Multiply by 4*
* or 0.4, 40, 400, etc.
To multiply a number by four, double it and then double it again! Remember to disregard any decimal points or zeros when starting the calculation.
Read more…
Trick No. 5 – Multiplying and Dividing with Decimal Points
This trick actually incorporates a few other tricks. Some we’ve already learned. One in particular is brand new, and another isn’t so much a trick as a sensible approach…
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The Learning Triangle
I’ve been reading What Counts? by Brian Butterworth. It’s a very worthwhile read for anyone interested in the psychology of learning. The book’s subtitle “How Every Brain is Hardwired for Math*” is appropriate, but not quite complete. I think Mr Butterworth’s book, although aimed at understanding the mathematical brain, goes a long way to explain learning in general. Read more…
Trick No. 4 – Squaring a Number
I read this trick in a book called What Counts? by Brian Butterworth.
To square a number, say “N”, add a small number “a” to it to make it a round number.
Then find (N+a) x (N-a) +a².
Here are some examples: Read more…
Trick No. 3 – Multiplying Positive and Negative Numbers
This is a great mnemonic (way of remembering) what the sign of your answer should be when multiplying positive and negative numbers:
Think:
good = pos
bad = neg
Read more…
Maths Blooper No. 1
This is just one example of some very funny errors I found on the “OnlineMathLearning.com” Web site.
(√5 + 1)/2
This number is called the “Golden Ratio”, or the “Divine Proportion”. The Penguin Dictionary of Curious and Interesting Numbers has 4 ½ pages dedicated to this number. It’s really popular among mathematicians, but artists also find it interesting and very useful. Read more…
Trick No. 2 – Dividing with Zeros
Numbers ending in zeros are just multiples of ten (or one hundred, or one thousand…) To divide with a number ending in zeros, ignore the zeros, do your division, then cancel the same number of zeros from the left and the right of the problem* Read more…
What’s a Googol?
These days, “Google” is a well-known search engine on the Internet. The name “Google” is a play on the word Googol*, which is the name for a number written as 1 followed by 100 zeros!
It looks like this:
10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
It’s easy to write it out; doesn’t take long at all. But if you had a googol pennies you couldn’t count them all in your lifetime. In fact, you couldn’t count them in a million lifetimes!
Here’s another number: a Googolplex, which is a 1 followed by a googol zeros. That’s so big it can’t even be written out in a million lifetimes!
*”1997: Larry and Sergey decide that [their] search engine needs a new name. After some brainstorming, they go with Google — a play on the word “googol,” a mathematical term for the number represented by the numeral 1 followed by 100 zeros. The use of the term reflects their mission to organize a seemingly infinite amount of information on the web.”
A Moral Tale*
There have been many claims for horsed that could count, but Sugar left them all far behind. He could count to one hundred, and also add, subtract, multiply and divide. Unfortunately, his master decided to try him on some elementary anaylytic geometry, which so frightened him that he ran off and was never seen again.
Moral: Never put Descartes before the horse.
*Taken from The Penguin Book of Curious and Interesting Mathematics, by David Wells