[alt-photo] Math mystery

[Jacques Kevers]

Hi,
I have a problem to understand the math behind this (related to making a
hardening solution with formalin):
"Add 25ml of formalin to 1,000ml of distilled water which makes a 3%
formalin hardening solution."
I mean, even if the formalin is 100% pure, 25 ml on 1000 is only 2.5% ,
right?
So, when using a 37% solution of formalin, I would think that you have to
use around 80ml of the formalin solution...
What am I missing?
Thanks,
Jacques