=+50. A random sample of smokers was obtained, and each individual was classified by both gender and age when he or she first started smoking. The data in the accompanying table is consistent with summary results reported in the article “Cigarette Tar Yields in Relation to Mortality in the Cancer Prevention Study II Prospective Cohort” (British Med. J., 2004: 72–79).

Gender Male Female

,16 25 10 Age 16–17 24 32 18–20 28 17

.20 19 34