Neurological research has shown that in about 80% of people language abilities reside in the brain s left side. Another 10% display right-brain language centers, and the remaining 10% have two-sided language control. (The latter two groups are mainly lefthanders.) (Science News, 161, no. 24 [2002])
a) We select 60 people at random. Is it reasonable to use a Normal model to describe the possible distribution of the proportion of the group that has left-brain language control? Explain.
b) What's the probability that our group has at least 75% left-brainers?
c) If the group had consisted of 100 people, would that probability be higher, lower, or about the same? Explain why, without actually calculating the probability.
d) How large a group would almost certainly guarantee at least 75% left-brainers? Explain.