Not enough info. As far as I am concerned, you are starting that each worker gets 600 dollars per week. That would make the answers to each of your problems the same: 0%.
there are 1000 factory workers earning up to 600 dollars per week.
if three of the workers are randomly selected, what is the probability that (a) all three earn less than 350 dollars, (b) two earn over 410 dollars and (c) at least one earns less than 240 dollars.
A) Probability all three earn less than 350 is
B) Probability that two earn over 410 dollars... is this exactly two, at least two, or at most two?
C) Probability that one earns less than 240 dollars is ,
Probability that at least one earns less than 240 dollars is