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ZackFlag for Canada

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PHP Math equation problem

Hi - I'm programming in PHP.  Here is some YTD information:
2011 YTD 14,989.3 2,877,688.8 $73,101.97
2010 YTD 18,409.8 1,911,203.4 $52,875.36
YTD Change Down 1.228% Up 1.506% Up 1.383%

The YTD Change % looks incorrect to me.  This is the formula I'm using to calculate the percentage.  I know you mathematical people will be horrified but I never did very well in math. :(  Help!

Thanks - Zack
if ($LMTDYYYAVG100 > $CMTDYYYAVG100) { $chMTDAVG100="<font color=red>Down " . number_format(($LMTDYYYAVG100/$CMTDYYYAVG100)*1, 3) . "%</font>"; } else { $chMTDAVG100="<font color=green>Up " . number_format(($CMTDYYYAVG100/$LMTDYYYAVG100)*1, 3) . "%</font>"; }
if ($LMTDYYYJet > $CMTDYYYJet) { $chMTDJet="<font color=red>Down " . number_format(($LMTDYYYJet/$CMTDYYYJet)*1, 3) . "%</font>"; } else { $chMTDJet="<font color=green>Up " . number_format(($CMTDYYYJet/$LMTDYYYJet)*1, 3) . "%</font>"; }
if ($LMTDYYYSPI > $CMTDYYYSPI) { $chMTDSPI="<font color=red>Down " . number_format(($LMTDYYYSPI/$CMTDYYYSPI)*1, 3) . "%</font>"; } else { $chMTDSPI="<font color=green>Up " . number_format(($CMTDYYYSPI/$LMTDYYYSPI)*1, 3) . "%</font>"; }

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TommySzalapski
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For down, the formula is a little reversed. Basically, you just subtract from 1 instead of subtracting 1.
(1 - ThisYear/LastYear)*100
I'll attempt to fix the code to show what I mean (I'm not the best at PHP so here goes):
if ($LMTDYYYAVG100 > $CMTDYYYAVG100) { $chMTDAVG100="<font color=red>Down " . number_format((1 - $LMTDYYYAVG100/$CMTDYYYAVG100)*100, 3) . "%</font>"; } else { $chMTDAVG100="<font color=green>Up " . number_format(($CMTDYYYAVG100/$LMTDYYYAVG100 - 1)*100, 3) . "%</font>"; }
if ($LMTDYYYJet > $CMTDYYYJet) { $chMTDJet="<font color=red>Down " . number_format((1 - $LMTDYYYJet/$CMTDYYYJet)*100, 3) . "%</font>"; } else { $chMTDJet="<font color=green>Up " . number_format(($CMTDYYYJet/$LMTDYYYJet - 1)*100, 3) . "%</font>"; }
if ($LMTDYYYSPI > $CMTDYYYSPI) { $chMTDSPI="<font color=red>Down " . number_format((1 - $LMTDYYYSPI/$CMTDYYYSPI)*100, 3) . "%</font>"; } else { $chMTDSPI="<font color=green>Up " . number_format(($CMTDYYYSPI/$LMTDYYYSPI - 1)*100, 3) . "%</font>"; }

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ASKER

That worked perfectly!!  Thanks!!  Just one question why do you have to -1 (subtract 1) from the back or from the front?  What does it do to the answer?

Apprecaite it!
Thanks!
The number you generate is the ratio of the new number to the old number. To see the change, you subtract the old number. It's the same as (new - old)/old. With a little algebra, you can see that they are identical.
If you lost 10%, this would actually give you a value of -10% gain. But you want to show the number as positive, so we flip it - (new - old)/old = (-new + old)/old = (old - new)/old = 1 - new/old.
I just short cut the algebra.
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Thanks for the explanation! I'm horrific in algebra. :(

Zack