Scribe Proability

Today in class we talked about different problems that can be solved,and different rules that apply.

If the question doesn't talk about telephones, then the First digit can't be a 0.

Example:
How many four-digit even number are there if the same digit cannot be used twice?



If the question talks about telephones then the first digit can be a 0.

Example:
2) The last part of your telephone number contain four digit how many such four-digit number there

10 * 10 * 10 * 10
__ __ __ __ = 10000

When the questions deal with Letters,In the rules , it can't be repeated nomatter what.

Example:

How many ways can the letters of the word FERMAT be arranged?

6 *5 *4*3*2*1

_ _ _ _ _ _ = 720

it can be display as 6!

Another faster way would be:

This way is called "Pick" Formula

nPr = n!/(n-r)!

n is the number of objects available to be arranged

r is the number of objects that are being arranged
6P6= 6!/(6-6)!= 6!/0!=720

When the question has the same letters, you would have to put them to together , because they can't be switch around, its impossible.

Example:

BOOK

4!/2! = 12

4!: is the numbers of letters.
2!: is the numbers of the same letters.

Remember when enter this question on the calculator you would have to be careful.

Example:

Putting this on calculator is correct:

11!/(2!4!4!)

Putting this on caluclator is incorrect:

11!/2!4!4!