expected number of survivor is 83?

I assume that every one in the row has complete information of the people before him.

for a group of three person, person 1 says black if person 2 and 3 has hat of the same colour and white otherwise. Then person 1 has 0.5 chance of surviving while person 2 and 3 will survive for sure.

this is in fact the highest rate of survival i have found so far, 2.5 out of 3, among any n people.

for a group of 4 person, person 1 says the colour of hats which is most dominant, shared by at least two people. I think it may yield better survival rate than simply 3, but it cant.

so the best answer i have so far is in a file of 100 people, let us have 33 groups of three person and one left. the total expected number of survivor is 83 in this case.