Theory question 105
ProbabilityThree red balls, five green balls and a number of blue balls are put together in a sack. One ball is picked at random from the sack. If the probability of picking a red ball is 1/6, find: (a) the number of blue balls in the sack; (b) the probability of picking a green ball.
Show the model answer
Model answer
(a) Let the number of blue balls be n; total = 8 + n
3/(8 + n) = 1/6 → 8 + n = 18 → n = 10
(b) Total = 18 balls, 5 green
P(green) = 5/18
Explanation
Use P(red) = red balls ÷ total balls to find the total first.