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dtbaker
Moderator
says

It’s Saturday night and my brain isn’t working too well. Anyone here good at Math?

I would like to solve Y in the below:

Y + (Y * 10%) + (Y * 10%) + (Y * 10%) = 3.9
so that is:
Y + (Y * 10/100) + (Y * 10/100) + (Y * 10/100) = 3.9

Y is 3. But given the above “3.9” value how could I come to “3”?

Thanks smart people!

Cheers,
Dave

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FinalDestiny
says

100Y / 100 + 10Y / 100 + 10Y / 100 + 10Y / 100 = 3.9

130Y / 100 = 3.9

130Y = 390

Y = 3

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gbs
says

Basically you have:

Y + 0.1 * Y + 0.1 * Y + 0.1 * Y = 3.9

=> 1.3 * Y = 3.9
=> Y = 3.9/1.3 = 3

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revaxarts
says

well, if Y = 3 the equation is 3.9:

Y + (Y * 10/100) + (Y * 10/100) + (Y * 10/100)
http://www.wolframalpha.com/input/?i=Y+%2B+%28Y+*+10%2F100%29+%2B+%28Y+*+10%2F100%29+%2B+%28Y+*+10%2F100%29

3 + (3 * 10/100) + (3 * 10/100) + (3 * 10/100)
http://www.wolframalpha.com/input/?i=3+%2B+%283+*+10%2F100%29+%2B+%283+*+10%2F100%29+%2B+%283+*+10%2F100%29

Edit: links didn’t work :)

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kriskorn
says

Here you go:

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dtbaker
Moderator
says

Good stuff!

Now to kick it up a level:

Y + (Y * A/100) + (Y * B/100) + (Y * C/100) = D

I will know A, B, C and D, but I will not know Y.

A, B, C are likely to be different (and not 10 as above example).

Could this be solved in a PHP script (if A, B, C and D are given)?

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dtbaker
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says
y + (y * 14/100) + (y * 13/100) + (y * 9/100) = 6.8
y + .14y + .13y + .9y = 6.8
1.36y = 6.8
6.8 / 1.36 = 5

solved for y = 5 sweet

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permian
says

y = d/[1+0.01*(a+b+b)]

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revaxarts
says
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permian
says

I mean,
$y = $d/(1+0.01*($a+$b+$c));

by
by
by
by
by
by