Question

Question 3)

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 fraternal twins?
Part C. If there are 5 sets of twin girls, what is the probability that at least four of the sets are identical twins?

Question 4)

The number of pill bugs found in a 1 meter by 1 meter area is thought to be normally distributed with a mean of 10 and standard deviation of 2. If 10 such areas are investigated, what is the probability that there are more than 110 pill bugs in total?

Answer 1

In Question 3, it is given that "we assume each sex the probability is 2."

Please confirm, because probability always lies between 0 to 1.