Divide the number of possible outcomes by the number of total outcomes.
Green: ≈ 0.55
Red: = 0.45
Since only red counters were added, this changes the probability of the counter being red to 0.6 or 60% and the probability of it being green to 0.4 or 40%. This means that the change in probability for the red counters was 15% or 0.15.
Set up a proportion:
, so x = 1.65, which rounds to 2 red counters.
We can prove this by adding 5 + 2 red counters. 7/11 = 0.6 or 60% chance.
Your final answer is 2 red counters were added.
Hope this helped. Get well soon.