The difference of twice a number and 9 is at least -20
Let's call the number "x".
Twice the number is 2x.
The difference of twice the number and 9 can be represented as 2x - 9.
According to the given statement, we have the inequality 2x - 9 ≥ -20.
To solve this inequality, we can add 9 to both sides:
2x - 9 + 9 ≥ -20 + 9
2x ≥ -11
Finally, we divide both sides by 2:
2x/2 ≥ -11/2
x ≥ -11/2
Therefore, the number "x" is at least -11/2.