2/5
Since 12 out of 30 marbles were black, you can assume that the percentage of black marbles in the bag is 40% (Ex: 12/30=.4) The probability that the marble you pick is black is equal to the percentage of black marbles in the bag. 40% is equal to 2/5.
Answer:

Step-by-step explanation:
Here,
f(x) = y

or , swapping x with y

now to solve for y we get

now we put f inverse x instead of y

I am done.
Answer:
if im correct it should be 40
Step-by-step explanation:
x=8+sqrt-8/12, x=8-sqrt-8/12
I think...