A bulb-manufacturing company kept a record of the number of hours it can glow before a bulb needed to be replaced. The following table shows the results of 500 bulbs:

If you buy a bulb of this company, then find the probability of the following events:
(a) The bulb needs to be replaced before it glows for less than 1500 hours.
(b) The bulb needs to be replaced when it glows between 1500 hours and 5000 hours.
(c) The bulb lasts for more than 2500 hours.

Explanation

Total number of bulbs tested =500.
(a) Number of bulbs replaced for less than 1500 hours = 10
p(bulb to be replaced before it glows for `lt` 1500 hours) `=(10)/(500)=0.02`
(b) Number of bulbs replaced between 1500 hours and 5000 hours = 150+250=400
p(bulb to glow between 1500 hours and 5000 hours) `=(400)/(500)=0.8`.
(c) Number of bulbs that last for last for more than 2500 hours =250+90=340
p(bulb lasts for more than 2500 hours) `=(340)/(500)=0.68`