Strange PHP IF Condition Equal [duplicate]

This question already has an answer here:

• Compare floats in php 17 answers

I'm having very strange problem.. My code is below:

$pRate = (double)str_replace(array("x+(x*", "/100)"), "", $p['formula']); // Formula = x+(x*22.5/100)

for($i=20;$i<=30;$i+=0.5){ 
    if($pRate == $i) echo "exists";
}

Why doesn't this code print "exists"? I checked the variable types with gettype. They are bot double. I printed all variables but 22.5 == 22.5 doesn't work?