what is this 'method' called? maths

Soldato
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14 Dec 2005
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this is probably basic but it's doing my head in!

8000*4 = 3800*x finding x with cross multiply and divide makes sense...
8000*4 = 3800*x so 32000 = 3800*x so x = 32000/3800 = 8.42105

this method also works, but struggling to see exactly why!
3800/8000 = 4/x so 3800/8000 = 0.475, then 4/0.475 = 8.42105
 
The "method" is simply reorganisation of the equation. In your first solution you reorganise so x is on the right-hand side. In your second you move x over to the left hand side, but then wrote it with the x term on the right:

1. (8000*4) / 3800 = x (divided both sides by 3800)
2. 4 / x = 3800 / 8000 (divided both sides by x, then divided both sides by 8000)
 
meant to write this as the first one...don't thnk it make any difference tho

3800 = 4
8000....x (ignore the dots!)

3800/8000 = 4/x finding x with cross multiply and divide makes sense...
8000*4 = 3800*x so 32000 = 3800*x so x = 32000/3800 = 8.42105
 
Last edited:
ok, thanks for that :p

maybe a better question would be how would you solve x...the most straight forward way of writing out the solution would be?

3800 = 4
8000....x
 
maybe a better question would be how would you solve x...the most straight forward way of writing out the solution would be?

3800 = 4
8000....x

That isn't a solution though, you're no better off there than you were beforehand, if anything you're slightly worse off.

Just divide by 3800 and you've got your equation for x.
 
Could also rearrange it to:

x - x/20 = 8

20x - x = 160

100x - 5x = 800

Then you can guess a few values of x with relatively easy to mentally calculate sums and converge on an approximate solution, if no calculators etc on hand. Factor of 100 used to make the sums easier. Accuracy to 2 decimal places not difficult with this particular equation.

BTW, I'm not sure it is allowed to show the Duckworth-Lewis method calculation in its raw form, probably will get Michael Vaughan coming after you with a cricket bat for revealing the secret.
 
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