The printf statement doesn't change the value it's printing, just the format. Thus, formatting 1500 with 2 decimal places should do exactly what you described it doing: printing 1500.00.

I do not really understand what you mean by avoiding "doing math" ... why do you not want to use math (as far as I know, you pretty much have to do math to meaningfully and reliably generate the output you desire). Perhaps you mean that you do not want to alter the value of $foo to generate the output, and also do not want to generate a new variable just for output formatting. If so, that is simple enough:

$foo = 1500;
printf ("%.2f", $foo/100);
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This generates the desired output without affecting the value of $foo and without using another variable. Yes, you have still multiplied by 0.01, but that value is only used for the printf output and then vanishes.

-HZ