Challenge Me!

Here's a Maths challenge for you to try over the Easter holiday: 

Calculator Bingo

This game is for you to play against the computer. However, you could easily use your own calculators and adapt it to play away from a computer.
The object of the game is to be the first to get exactly to zero.
How to play:

1. Enter a 7-digit number into your calculator. You may use the same digit more than once. The computer will also put a number into its calculator.
2. A random number will appear at the top of the screen. If this digit appears in the number you have on your calculator, you can change that digit to zero by subtracting the appropriate number using the calculator keys.
3. If you subtract the correct amount, this digit will automatically change to zero. If you are incorrect, you will be allowed another chance.
4. For every random number given, you can only remove one digit from your calculator. So if you have, for example, four 3's you must wait for 3 to come up four times.
5. The computer will do the same thing as you for each number.
6. The first to reach exactly zero is the winner.