SOLUTION: A bin contains 75 light bulbs, 5 of which are defective. If 5 light bulbs are randomly selected from the bin with replacements, find the probability that all the bulbs selected ar

It means that you, actually, select your bulbs from the set of 70 good bulbs.


Therefore, you may find the probability as


    P =  = 0.70124  (rounded).    ANSWER


The formula says that you first select any of 70 good bulbs from the total of 75 bulbs;

then you select any of 69 remaining good bulbs from the total of remaining 74 bulbs;


    . . . and so on 5 times, in all, completing your selection.



If you are familiar with the notion/conception of COMBINATIONS, you may write the formula for probability in this way


    P = ,


which says that the total space of events contains    elements,

while the space of favorable events has   elements.



Both formulas produce the same value and the same answer.