Name: fiza

Who is asking: Student
Level: Secondary

Question:

To use telephone banking to pay bills, the customer has to enter the last three
digits of each bill. the numbers 0 to 9 can be used. if the number happened to
be the same on more tan one bill, the customer has to enter the first three
digits as well.

(a) what is the probability that a person has 2 bills to register with the same
last three digits?

ANSWER:P(2 bills to register)=1/10P3
1/(10!/7!), 1/(10*9*8)=.001389

(b) what is the probability that a person with 10 bills to register has at least
2 bills with the same last three digits?

ANSWER:P=1/(10*10*10)
=0.001

Hi Fiza,
Use the negation: All bills have different last three digits.

We have 1000, three digit numbers, so for (b)

P=(1000/1000)*(999/1000)*(998/1000)*...*(990/1000)=
whatever. After this subtract the obtained number from 1.

Andrei