Question:
80 bulbs are selected at random from a lot and their lifetime in hours is recorded as under.
One bulb is selected at random from the lot. What is the probability that the selected bulb has a life more than 500 hours?
(a) $\frac{27}{40}$
(b) $\frac{29}{40}$
(c) $\frac{5}{16}$
(d) $\frac{11}{40}$
Solution:
(b) $\frac{29}{40}$
Explanation:
Total number of bulbs in the lot = 80
Number of bulbs with life time of more than 500 hours = (23 + 25 + 10) = 58
Let E be the event that the chosen bulb's life time is more than 500 hours.
$\therefore$ Required probability $=P(E)=\frac{58}{80}=\frac{29}{40}$
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