The math here, for those wondering, is that “informed host has a 0 chance to pick the car” becomes “ignorant host has a 1/3 chance to pick the car”. Contestant’

The math here, for those wondering, is that “informed host has a 0 chance to pick the car” becomes “ignorant host has a 1/3 chance to pick the car”. Contestant’s original pick is still 1/3 and the unpicked door goes from 2/3 (informed) to 1/3 (ignorant).