Answer:
15
Step-by-step explanation:
Total: n counters
Blue counters: 1
Red counters: n - 1
a)
You can take a blue counter first followed by a red counter, or a red counter first followed by a blue counter. We find the probability of each and add them.
Take a blue counter first:
p(blue) = 1/n
Take a red counter second:
p(red) = (n - 1)/(n - 1)
p(blue and red) = 1/n * (n - 1)/(n - 1) = 1/n
or
Take a red counter first:
p(red) = (n - 1)/n
Take a blue counter second:
p(blue) = 1/(n - 1)
p(blue and red) = (n - 1)/n * 1/(n - 1) = 1/n
Add the two probabilities above:
1/n + 1/n = 2/n
The probability you pick a counter of each color is 2/n
b)
We are told the probability of picking one counter of each color is 0.125
2/n = 0.125
2 = 0.125n
n = 2/0.125 = 2/(1/8) = 16
n = 16
red counter: n - 1 = 16 - 1 = 15
