Question

The number of different $7$-digit telephone numbers that can be formed by using $0,1,2,3,4,5,6,7,8,9$ is :

• A. ${10}^7$
• B. $9\times {10}^6$
• C. $9!$
• D. None of these

Answer 1

Answer: (A)

${10}^7$

For each digit in the $7$ digit number there are $10$ options

i.e there are $10$ possible numbers for each digit.

Hence the number of different $7$-digit telephone numbers will be

$10\times 10\times 10\times 10\times 10\times 10\times 10={10}^7$