Question

A pencil box has total 70 pencils ;15 red pencils, 20 blue pencils, 25 green pencils, and rest yellow pencils (total 70).

(a) What is the probability of picking a blue pencil?



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(b) You pick a green pencil and return it. What is the probability that the next one is red?





(c) You pick a yellow pencil and keep it. What is the probability that the next pencil will be green?

Answer 1

Total pencils = 70. Counts: red = 15, blue = 20, green = 25, yellow = 70 − (15+20+25) = 10.

(a) P(blue) = 20/70 = 2/7 ≈ 0.2857.

(b) If you pick a green and return it, the composition is unchanged, so P(next is red) = 15/70 = 3/14 ≈ 0.2143.

(c) If you pick a yellow and keep it, there are now 69 pencils with still 25 green, so P(next is green) = 25/69 ≈ 0.3623.