A box in a certain supply room contains five 40-W lightbulbs, four 60-W bulbs, a

Question

A box in a certain supply room contains five 40-W lightbulbs, four 60-W bulbs, and seven 75-W bulbs. Suppose that three bulbs are randomly selected. (Round your answers to four decimal places.) (a) What is the probability that exactly two of the selected bulbs are rated 75-W? (b) What is the probability that all three of the selected bulbs have the same rating? (c) What is the probability that one bulb of each type is selected? (d) Suppose now that bulbs are to be selected one by one until a 75-W bulb is found. What is the probability that it is necessary to examine at least six bulbs?

Explanation / Answer

A) P(exactly 2 bulbs are of 75W) = 3C2 x (7/16) x (6/15) x (9/14) = 0.3375

B) P(all have same rating) = (7C3 / 16C3) + (5C3 / 16C3) + (4C3 / 16C3)

= 0.0625 + 0.0179 + 0.0071

= 0.0875

C) P(one bulb of each type) = (5/16)(4/15)(7/14)x3! = 0.25

D) P(it is necessary to examine at least 6 bulbs) = P(no 75W bulb in among the first 5 bulbs selected)

= 9C5/16C5

= 0.0288

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.