what is this 'method' called? maths

builder22

builder22

builder22

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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
 
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This is the Duckworth-Lewis method. In this case the required run rate is 8.42 runs in 4 overs. Unless it continues to rain, in which case 8000 must be adjusted accordingly.
 
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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
 
builder22 said:
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
Click to expand...

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.
 
builder22 said:
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
Click to expand...
cross multiply (multiply both sides by 8000x)
3800x = 32000
then divide both sides by 3800 to get x=32000/3800
 
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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