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A new drug has been released and produces some minor side effects. 8% of users suffer only a loss of sleep and 12% of users suffer only bouts of nausea. 75% of users will have no side effects at all. What percentage of users will suffer from both loss of sleep and nausea?

What I learn in school is: if there is or in question then sum ($+$) , if there is and then multiply ($\times$)

Ans: $12*8=96$

and I have try many ways, I can't get the right answer 5%
I have no idea how to find the probability, please explain me. Highly appreciate it. thanks

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up vote 2 down vote accepted

You just need to add these numbers so out of 100 - (8 + 12 + 75) = 100 - 95 = 5%. Essentially we are accounting for percentage of people out of a group having a particular property, whatever is left are the bunch who have both since every one else who has been counted has only one specific property.

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