The given problem describes a binomial distribution with p = 60% = 0.6. Given that there are 400 trials, i.e. n = 400.
a.) The mean is given by:

The standard deviation is given by:

b.) The mean means that in an experiment of 400 adult smokers, we expect on the average to get about 240 smokers who started smoking before turning 18 years.
c.) It would be unusual to observe <span>340 smokers who started smoking before turning 18 years old in a random sample of 400 adult smokers because 340 is far greater than the mean of the distribution.
340 is greater than 3 standard deviations from the mean of the distribution.</span>
20×1=20
20×2=40
20×3=60
20×4=80
20×5=100
20×6=120
20×7=140
20×8=160
20×9=180
20×10=200
(Only include this if the table is up to 12)
20×11=220
20×12=240
Sara's results probably do have a higher mean, if we take into account how William is way more willing to pay 20 dollars. Honestly, I think you got your chosen answers right! Just my opinion, as someone inexperienced.
the answer is 2,419,200 seconds