doing a maths night class, can any one in simple terms explain to me:

[dissle]

How to do percentages,
How to turn a fraction into a percentage and back?
How to do subtraction...yes really, i absolutely struggle and get a different answer each time i do them.

How to turn a fraction into a decimal number.

there HAS to be an easy way to do and remember these things.

[Blandmum]

gentle guide to percentages here

this site is helpful

[Blandmum]

For the suntraction think, how much less is the second number,

so 10-7=

How many less is 7 than 10? 3

10-7=3

20-10=

How many less is 10 than 20?

[dissle]

OH MY GOD>>>Perfect martian, thanks SO much...added it to my favourites, will keep doing it...

a million thankyous xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

[dissle]

with subtractions its the.....468
-376
that i struggle with, dont ask me why i just seem to get a different answer every time i do it. ??????

[DumbledoresGirl]

I could teach you subtraction dissle, (primary school teacher - must be able to teach that sort of subtraction in my sleep!-but not here - too complicated!

[DumbledoresGirl]

Do you use the borrowing technique? ie in your example, you can take 6 from 8 but get stuck when you get to the tens column as you can't take 7 from 6. You need to borrow a hundred from the hundred's column so you actually have 16 tens and take 7 tens from them. Then, your hundreds column only had 3 in the top number and 3 in the bottom which cancel each other out.

Told you it is complicated to explain here but dead easy to explain in person!

[dissle]

LOL! Dumbledore...you're allot of use!

No still dont get it, just looked at the website more closely, dont understand where the numbers come from?????

[throckenholt]

a percentage is a proportion of 100

• so 50% is 50/100 (50 out of 100) - which can also be written 0.50 or 1/2
  
• 85% is 85/100 or .85
  
  
  4/5 is the same as 80/100 or .8 or 80%
  
  
  If you don't have a calculator then you need to say - what do I have to multiply the bottom by to get to 100 (in the example above 5x20=100), then multiply to top number by that too (so 4x20=80), then you have 4/5 is the same as 80/100 which is 0.8 or 80%
  
  
  With substractions - add the answer you get to what you subtracted and you should get back to the original number (as a check)
  
  so 85-43 = 42 42+43 = 85
  
  
  any help ?

[witchandchips]

for the 468-376 example dissle round up or down the numbers to benchmark your answer

468-376 is rougly 470-380=90
so you know to expect an answer around 90

[dissle]

I do use the borowing method, yes.
I get confused when carrying over though...dont know where to add it IYSWIM

[dissle]

rounding up i can do, makes it easier in fact, you can then get an aproximation cant you...great for multiple choice questions.Thanks whichchips


OOOH Throcky, yes that makes sense, just let me have a go on a few by myself....see if i can get it..

[witchandchips]

another way (without the borrowing)

468-376
=
(460+8)-(370+6)
=
(460-370)+(8-6)
=
90+2=92

[throckenholt]

another way to do substraction - eg 468-376

start at 376 - how many do you have to add to get to 468 - so you need 2 to get to 8, -10 to get from 70 to 60, and 100 to get from 300 to 400, so add them together 2-10+100=92

check 92 + 376 = 468

[Blandmum]

468
376-
--

first take 6 from 8= 2

You cab't take 7 from 6, becayuse 7 is bigger than 6.

You borrow one from the next column along, and make the 7, 17 (because the next colum along is 10 time bigger, so 1 from there = 10 IYSWIM)

You can now take 8 from 17= 9

Beause you borroed one you have to pay it back, and you put that on the bottom and add that on to the 3, which makes it a 4. 4-4=0

468
376-
1
-
092

[dissle]

trying to do 63% except i cant work out what goes into 100 and what goes into 63 to cancel down.
Help?

[dissle]

LOVE that way wichychips, that is so easy.

[witchandchips]

think my way is easier

[Blandmum]

63%=

63
---
100

[dissle]

so its 63%= 0.63
or63/100, how do you make it smaller tho?

[CountessDracula]

It has to be divisible to make it smaller

eg 50/100 is the same as 5/10

so 63 is divisble by 3 (3 x 21 = 63)

Howeever as 100 isn't divisible by 3 you can't use it (or would be 21/33.333333 which is not nice!)

[witchandchips]

63%=63/100

63 has no "common factors" with 100
so 63/100 can't be simplified

common factors = whole numbers that be divided into both numbers
so 2 is a common factor of 4 and of 8

another example
65%=65/100
common factor = 5

65/5 = 13
100/5 = 20
65/100 = 13/20
13 has no common factors with 20 so stop

[CountessDracula]

witchandchips said it much better than me!

[dissle]

ahhh thats why i couldnt do it..brilliant! thanks.

[dissle]

so its the number which will divide into both numbers. BUT it has to be divisable or you just leave it alone...is that right?

[Blandmum]

you can't, because 63/100 is 0.63

you can make a fraction smaller if you can divide the top and bottom numbers by something, and end up with a whole number answer

so 10/100 is the same as 1/10 (you can difide them both by 10). And both of these are 0.1