Final answer:
To find the number of green marbles in the box before doubling, we need to set up two probability equations using the given information. Solving these equations will give us the value of 'g'.
Step-by-step explanation:
Let's start by assigning variables to the number of green marbles and the probability of selecting a red marble. Let's say the number of green marbles is 'g' and the probability of selecting a red marble is 'x%'.
From the given information, we know that there are exactly four red marbles in the box.
Initially, the probability of selecting a red marble is 'x%', which means the probability is 0.01x.
Since the total number of marbles in the box is the sum of the green and red marbles, we can write the initial probability equation as 4/(g+4) = 0.01x.
When the number of green marbles is doubled, the new probability of selecting one of the four red marbles is '(x - 15)%', which is 0.01(x - 15).
At this point, the total number of marbles in the box is 2g + 4, so we can write the new probability equation as 4/(2g+4) = 0.01(x - 15).
We can now solve these two equations to find the value of 'g'.