How many ways to make number 9?

Answer 1

Infinitely many.

Start with sums of two whole numbers:

5+4, 6+3, 7+2, 8+1, 9+0, 10+(-1), 11+(-2), ... and infinitely more.

Then consider numbers to one decimal place (dp):

4.5+4.5, 4.6+4.4, 4.7+4.3, and infinitely more of those.

And then numbers with 2 dp, 3 dp, ... infinitely many dp.

Next, consider sums of 3 numbers, 4 numbers, 5 numbers, ... , infinitely many numbers - in each case using numbers with 1 dp, 2 dp, 3 dp, ... infinitely many dp.

When you have done all those you can start with multiplications.

And then move on to other mathematical operations.