a.A thief has stolen Roger's automatic teller machine (ATM) card. The card has a four-digit personal identification number (PIN). The thief knows that the first two digits are 8 and 6, but he does not know the last two digits. How many pin numbers are possible in this case? Explain which of the following rule (permutation/combination/counting rule ) you must apply to solve this problem.

b.What is the probability that the thief will find the correct PIN in its first try?

c.If the thief knew that the first two digits were 8 and 6 and that the third digit was either 1 or 7, 4th digit can be any number,in that case how many pin numbers were possible?