Question

How many 10 digits number can be written by using digits (9 and 2) ?

• A. ${}^{10}{C}_1{+}^9{C}_2$
• B. $2^{10}$
• C. ${}^{10}{C}_2$
• D. $10!$

Answer 1

The correct option is B $2^{10}$

Total number of numbers =2×2.....×102×2.....×10 times

⇒$2^{10}$

Hence (B) is the correct answer.