If you write plus signs between each of the digits $1$ to $9$, this is what you get:

$1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45$

However, if you alter where the plus signs go, you could also get:

$12 + 3 + 45 + 6 + 7 + 8 + 9 = 90$

Can you put plus signs in so this is true?

$1\;$ $2\;$ $3\;$ $4\;$ $5\;$ $6\;$ $7\;$ $8\;$ $9\;$ $= 99$

How many ways can you do it?