Phone numbers

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

Correct answer:

n =  544320

Step-by-step explanation:

$n=9\cdot 9\cdot 8\cdot 7\cdot 6\cdot 5\cdot 4=544320$

Try another example

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.

2 years ago  1 Like Like

Related math problems and questions:

• Permutations
  How many 4-digit numbers can be composed of numbers 1,2,3,4,5,6,7 if: and, the digits must not be repeated in the number b, the number should be divisible by 5 and the numbers must not be repeated c, digits can be repeated
• Digits
  How many five-digit numbers can be written from numbers 0.3,4, 5, 7 that is divided by 10, and if digits can be repeated?
• Numbers
  How many different 3 digit natural numbers in which no digit is repeated, can be composed from digits 0,1,2?
• Dd 2-digit numbers
  Find all odd 2-digit natural numbers compiled from digits 1; 3; 4; 6; 8 if the digits are not repeated.
• Digits
  How many odd four-digit numbers can we create from digits: 0, 3, 5, 6, 7? (a) the figures may be repeated (b) the digits may not be repeated
• Digits
  How many natural numbers greater than 4000 which are formed from the numbers 0,1,3,7,9 with the figures not repeated, B) How many will the number of natural numbers less than 4000 and the numbers can be repeated?
• Three digits number
  How many are three-digit integers such that they no digit repeats?
• Three-digit numbers
  We have digits 0,1,4,7 that cannot be repeated. How many three-digit numbers can we write from them? You can help by listing all the numbers.
• How many
  How many double-digit numbers greater than 30 we can create from digits 0, 1, 2, 3, 4, 5? Numbers cannot be repeated in a two-digit number.
• Inverted nine
  In the hotel Inverted Nine, each hotel room number is divisible by 6. How many rooms can we count with the three-digit number registered by digits 1,8,7,4,9?
• Three-digit numbers
  How many three-digit numbers are from the numbers 0 2 4 6 8 (with/without repetition)?
• Three-digit numbers
  Use the numbers 4,5,8,9 to write all three-digit numbers without repetition. How many such numbers are there?
• Four-digit numbers
  How many four-digit numbers can we make from the numbers 2, 6, 3, 5, 1 and 9 if the numbers in the number cannot be repeated?
• Telephone numbers
  How many 7-digit telephone numbers can we put together so that each number consists of different digits?
• Three digits number
  From the numbers 1, 2, 3, 4, 5 create three-digit numbers that digits not repeat and number is divisible by 2. How many numbers are there?
• Five-digit
  Find all five-digit numbers that can be created from numbers 12345 so that the numbers are not repeated and then numbers with repeated digits. Give the calculation.
• Divisible by five
  How many different three-digit numbers divisible by five can we create from the digits 2, 4, 5? The digits can be repeated in the created number.