Answer:
-4.5
Explanation:
You arrange the numbers from lowest to highest value:
-17, -12, -11, -10, -7, -2, 7, 10, 16, 20
Then you find the one in the middle:
-7, -2
Because there are two in the middle, you add them and divide them by two:
(-7 + -2)/2 = -4.5
Your answer is -4.5.