Flip a coin 6 times and 2 heads are obtained. In how many different ways can this occur?

Two discrete random variables X and Y have a joint probability function f(x,y) given in the following table.        f(x,y) y=0 1 2 x=1 0.30 0.12 0.18 2 0.20 0.12 0.08  Find the probability P(X+Y>2).

Put digits  1, 2, 3, 4 and 5 in a random order to form a 5-digit number.    What is  the probability of getting an even number?   

A football team will play one game with each of other six teams.  The team won four games and lost twice.  In how many different ways can this happen?

Six different presentations have been scheduled in six time slots:   8:00-9:00, 9:00-10:00, 10:00-11:00, 11:00-12:00, 2:00-3:00, and 3:00-4:00.   Suppose you are allowed to attend four presentations.  How many different choices do you have if you attend exactly four presentations? 

Which type of blood cell is primarily responsible for fighting infection?

Which disorder is associated with iron-poor blood?

What are the two types of passive immunity?

Which blood vessel carries oxygen-rich blood from the lungs to the heart?

Which of the following are the major ABO blood types?