If we're going to be bluffing 7.50 into $10.

From villains point of view, he's facing a 7.50 call in a 17.50 pot, so he's getting 17.50:7.50 pot odds, or 2.33:1, so villain needs to be good 30% of the time when he makes the call.

This means that hero should have 30% bluffs and 70% value. At least that's been my understanding?