If a camera lens is randomly selected from the general population of all camera lenses, what is the
Mathematics

Tutor: None Selected  Time limit: 1 Day 
Lens  Defective  Not Defective  Total 
Greens  5%  55%  60% 
Parsons  10%  5%  15% 
Ratten  6%  19%  25% 
Total  21%  79%  100% 
I think you need to post the rest of the question there are a few outcomes to probability questions like this. But! I shall solve the question for all variables, and then we'll work it out afterwards if need be.
The likelihood of selecting a lens that is defective is determined by two factors:
1) The likelihood of selecting one company over another
2) The percent chance of getting a defective lens from that company.
Probability of selecting a Greens Lens: 60/100
Probability of selecting a Parsons Lens: 15/100
Probability of selecting a Ratten Lens: 25/100
So, from that list, we then multiply against the defect rate to determine the likelihood of selecting a company AND a defective lens:
Probability of selecting a defective Greens Lens=(3/5)*(1/25)=3/125
Probability of selecting a defective Parsons lens=(3/20)*(1/10)=3/200
Probability of selecting a defective Ratten Lens=(1/4)*(3/50)= 3/200
I cannot tell from the answer you posted whether or not you needed defective or nondefective rates, so here are the nondefective probabilities:
Probability of selecting a NONdefective Greens Lens=(3/5)*(11/20)=33/100
Probability of selecting a NONdefective Parsons lens=(3/20)*(1/20)=3/400
Probability of selecting a NONdefective Ratten Lens=(1/4)*(19/100)=19/400
Secure Information
Content will be erased after question is completed.