# Phone numbers

How many 7-digit telephone numbers can be compiled from the digits 0,1,2,..,8,9 that no digit is repeated?

**Result****Leave us a comment of example and its solution (i.e. if it is still somewhat unclear...):**

**Showing 1 comment:**

**Mathyu**

Solution is not correct. 0-9 is 10 digits, so n = 10 * 9 * 8 * 7 * 6 * 5 * 4 = 604800. Or, 10!/3! = 604800. If there was a restriction on the first digit, such that the first digit could not be 0 or 1, or any other number, then it would be 9. However, there is no restriction (that is given) to make this valid, so for the first digit, there are initially 10 digits to choose from. After one is taken, then it goes to 9 and etc.

#### To solve this example are needed these knowledge from mathematics:

## Next similar examples:

- Stacks

Annie has a total of $ 702. The money must be divided into stacks so that each buyer has the same amounth of dollars. How many options she have? - No. of divisors

How many different divisors has number ?? - Shelf

How many ways are there to arrange 6 books on a shelf? - Rectangles

How many rectangles with area 3032 cm^{2}whose sides is natural numbers are? - Candy

How many ways can divide 15 identical candies to 5 children? - Seating

How many ways can 5 people sit on 4 numbered chairs (e. G. , seat reservation on the train)? - Flags

How many different flags can be made from colors white, red, green, purple, orange, yellow, blue so that each flag consisted of three different colors? - 2nd class variations

From how many elements you can create 2450 variations of the second class? - Morse alphabet

Calculate how many words of Morse code to create compiling commas and dots in the words of one to four characters. - 7 heroes

9 heroes galloping on 9 horses behind. How many ways can sort them behind? - Vans

In how many ways can 9 shuttle vans line up at the airport? - Guests

How many ways can 5 guests sit down on 6 seats standing in a row? - Orchard

3 trees in 3 lines grows in the orchard. How many trees are in the orchard? - Football league

In the 5th football league is 10 teams. How many ways can be filled first, second and third place? - Playing cards

How many possible ways are to shuffle 7 playing cards? - Pairs

At the table sit 8 people, 4 on one side and 4 on the other side. Among them are 3 pairs. Every pair wants to sit opposite each other. How many ways can they sit? - Word

What is the probability that a random word composed of chars D, G, O will be the DOG?