Question

How many times does the digit 7 appear when you write from 11 to 100?

• A. 9
• B. 10
• C. 11
• D. 19

Answer 1

Answer: (D)

19

Let us count $7$ in $2$ ways, with $7x$ and $7y$ being numbers between $11$ and $100$.
For $7x$, x will take values from $1$ to $9-9$ values
For $7y$, y will take values from $0$ to $9-10$ values
Total: $9+10$ values = $19$.
The digit $7$ appears $19$ times when you write from $11$ to $100$