the maths thread mj 23 over here!

[MJ.23]

Also nice find with that calculator Nu. Personally I despise statistics! I have found several useful calculators in my time and will post some up for people to use.

One which people are probably familiar with is wolfram alpha:

If you are not; this is an incredibly effective way to prove if your answer is correct, Type it in; and it solves it.

Wolfram|Alpha: Computational Knowledge Engine

[DamianWalker]

thanks a lot mj, i did have an idea but i couldn't find anything through google to back my answer, as you cant just say something, you have to back it up and understand it. don't worry about the iterative method, no need to brush up on it for my sake, i'm sure il figure it out.

cheers.

[Mart001]

for odd multiplications I use a x10 rule... when you have to work something out on the spot "whats 7x9" bang! mutliply 7x10 then 10-9=1 then multiply this by the origianl number and minus 1x7= 93, "whats 16x8", 160x10=160, 16x2=32, 160-32=128...

This is alot less complicated when it goes on in my head

[MJ.23]

Quote

for odd multiplications I use a x10 rule... when you have to work something out on the spot "whats 7x9" bang! mutliply 7x10 then 10-9=1 then multiply this by the origianl number and minus 1x7= 93, "whats 16x8", 160x10=160, 16x2=32, 160-32=128...

This is alot less complicated when it goes on in my head

For the example of 16x8, I would do:

(10*8) + (6*8) = 128

[NU_nutrition_TS]

Quote

for odd multiplications I use a x10 rule... when you have to work something out on the spot "whats 7x9" bang! mutliply 7x10 then 10-9=1 then multiply this by the origianl number and minus 1x7= 93

I take it that bit in bold should have been 7x1=7, 70-7=63?

I have another method for any multiplication involving the number 9.

Using your example, 7x9: the first digit of the answer will always be one less than the number by which you are multiplying the nine, in this case 7-1=6. The second digit will be what ever you need to add to 6 to make 9, in this case 3 (6+3=9) so the answer is 63. Another example would be 9x9. The first digit would be 8 (one less than nine) and in order to make that up to 9 you have to add 1, so the answer is 81.

Of course, this only works for any multiplier up to ten (10x9: 10-1=9 (first digit of answer) add on 0 (second digit of answer)=90 (9+0=9). Once you go to eleven up to twenty you have to start subtracting two (15*9: 15-2=13 (first two digits of answer) and, in order for the answer to add up to nine again, you need to tack on a 5 (1+3+5=9) - so the answer is 135. Once you get to 21-30 you would have to subtract 3 (see the pattern?), e.g. 28x9: 28-3=25 (first two digits) and tack on 2 to make 252 (2+5+2=9)

In other words, the digits of any number that is a multiple of (or exactly divisible by) nine always add up to (including by reduction) nine. So the number 17,523 reduces (by addition of the digits) to nine, e.g., 1+7+5+2+3=18 and 1+8=9, therefore you know it is exactly divisible by 9 (17,523/9=1947). Sometimes this may include certain multiples of nine (such as 27) and a subdivision of nine: 3 (3x3=9), e.g., 17,523/27=649 and 17,523/3=5,841.

As Mart said - it sounds complicated - but once you see the pattern/understand the underlying principles, it can be done quite quickly in your head!

[blackstone]

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for odd multiplications I use a x10 rule... when you have to work something out on the spot "whats 7x9" bang! mutliply 7x10 then 10-9=1 then multiply this by the origianl number and minus 1x7= 93

Good spot Nu!

Quote

"whats 16x8", 160x10=160, 16x2=32, 160-32=128...

I think Mart is trying to confuse/trick us!

[ben 21]

sorry ive been quiet guys, im just going through a very painful break up at the moment. i half want to stick a gun in my mouth and blow half my head off. im never falling in love again! lol i,ll be back soon posting up some maths problems.

[ben 21]

is there a way i can divide fractions quickly? i strugled a bit with that.

[HBK]

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is there a way i can divide fractions quickly? i strugled a bit with that.

You could turn them into numbers, like 3/4 into 75, or 4/5 into 80. Would that help at all?

[ben 21]

yeah kinda, the thing is i get the basics down, then start doing it, then the teacher moves too fast and i lose confidence, then im back to where i started.