Recently a study was published that stated that: "40% of children are subjected to tobacco smoke in their home."
If we assume that all households consist of a father and a mother and one or more children, that children do not smoke and that smoking rates are the same for men than for women,
What percentage of adults are smokers?
The probability of receiving tobacco is that at least one of the parents is a smoker. This is equal to the sum of both probabilities minus their product (probability that both are). That is, if x is the smoking rate:
2x - x2 = 0,40
From where we easily get that x = 0.225, that is, 22.5% of adults are smokers.