Question

4. Thoughtful Politicians [This problem setting is due to Prof. James Norris of Cambridge University.] In a group of 100 politicians, 40 are in Party I and 60 are in Party II. Members of Party I are incapable of changing their minds about anything. Members of Party II change their minds completely randomly every day, independently of all others and also independently of all evidence. Tomorrow, the politicians are going to vote on Proposition 88. Here is a summary of their opinions today. Of the 40 members in Party I, 25 are in favor of Prop 88 and 15 are against. Of the 60 members in Party II, 10 are in favor and 50 are against. Assume that each member in Party II changes their mind based on the toss of a coin: if it lands heads they switch to the opposite opinion and if it lands tails they don't change their mind. a) What is the distribution of the number of members in Party II who will favor Prop 88 tomorrow

Answer 1

Explanation:

The focus is on Party 2, because as already said, Party 1 members NEVER change their minds on anything!

There are 60 politicians in Party 2. They change their minds completely-randomly every day.

Tomorrow, the politicians will vote on a proposition: Proposition 88, but today, 10 are in favor of it while 50 are against it.

Each member changes their mind based on the toss of a coin (a fair/unbiased coin; since it was not stated that the coin is biased). A fair coin has a 0.5 probability of landing HEADS and same 0.5 probability of landing TAILS.

What is the distribution of the number of members in Party II who will favor Prop 88 tomorrow?

The number of figures in the distribution will depend on the number of times the coin is tossed, between today and tomorrow.

KEY: Assuming the coin is tossed 12 times between today and tomorrow AND assuming that half of the time - 6 times - it landed HEADS and half of the time, TAILS (Head and Tail simultaneously).

Beginning with HEADS, the distribution of the number of members who will favor the proposition tomorrow, is:

50, 10, 50, 10, 50, 10, 50, 10, 50, 10, 50, 10