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.