An inspector is checking a sample of lightbulbs for defects. The following table

Question

An inspector is checking a sample of lightbulbs for defects. The following table summarizes her findings.

Wattage     Good       Defective    Total

20                80              15            95

50                 100              5           105

100               120             10          130

Total             300             30           330

Find the probability that the light bulb is good given that it is 50 watts.

105/330 = 7/22

100/300 = 1/3

100/105 = 20/21

None of the above

105/330 = 7/22

100/300 = 1/3

100/105 = 20/21

None of the above

Explanation / Answer

Its given that the bulb is of 50 watts, therefore, total number of 50 watts bulbs = 105, and the total number of good 50 watt bulbs = 100

Probability (good bulbs of 50 watts) = favourable number of bulbs / Total number of bulbs= 100/105= 20/21

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