1 out of 1000 births results in fraternal twins; 1 out of 1500
births results in identical twins. Identical twins 1
must be the same sex but the sexes of fraternal twins are
independent and we assume each sex the probability is 2.
Part A. Build the corresponding tree diagram.
Part B. If two girls are twins, what is the probability they are
Part C. If there are 5 sets of twin girls, what is the probability
that at least four of the sets are identical twins?