Question

How many $9$ digit mobile numbers can be formed if a digit can be repeated any number of times?

• A. ${}^{10}{P}_9$
• B. $9\times {10}^8$
• C. ${}^{10}{C}_9$
• D. ${10}^{10}$

Answer 1

The correct option is B $9\times {10}^8$

Each blank can be filled with any

$9$ Digit mobile number

$0,1,2,3,4,5,6,7,8,9$

Number of ways of filling each blank number of digits is ten

Therefore total number of mobile numbers

$\Rightarrow 9\times 10\times 10\times 10\times 10\times 10\times 10\times 10\times 10\Rightarrow {9\times \left(10\right)}^8$

Option $:B$