Answer to Question #340134 in Statistics and Probability for Maneo

Question

In a class, 70% of all students are boys and the rest are girls.

• 10% of the girls are smokers

• 20% of the boys are smokers

1) Find the probability that a randomly selected student is a smoker.

Answer 1

There are 30% girls in the class (because 70% of all students are boys).

• 10 percent of 30 is $30*10/100=3$ % (girls smokers)
• 20 percent of 70 is $70*20/100=14$ % (boys smokers)

So, the probability that a randomly selected student is a smoker is $3+14=17\%$ $=0.17$