I'll take a stab at it, but wait for confirmation from others before taking my 
word for this:

If you dilute it 10 to 1, that ought to bring it down to 3.5%.  One part h2o2 
in 10 parts water.

If you want to be more exact, one part h2o2 to 11.7 parts of water would get 
you closer to 3%.

Dick




________________________________
From: Kirsteen Wright <kirsteen.falcons...@gmail.com>
To: silver-list@eskimo.com
Sent: Fri, March 5, 2010 12:41:45 PM
Subject: CS>Food grade hydrogen peroxide

OK this may sound like a stupid question. I have food grade H202 35%. The brain 
fog has fully set in. What ratio of this to distilled water do I use to get it 
down to 3%?  I sem to have forgotten all the maths I ever learnt.

Cheers
Kirsteen (obviously a bear of very little brain)