A hint to get started
Find a central height interval and a large-sample tail limit
Girl heights are normal with mean 155 cm and standard deviation 10 cm. Find
(i) the symmetric interval about the mean containing 40% of heights, marks
(ii) the probability exactly two of four randomly chosen girls exceed 170 cm, marks
(iii) the probability that the total height of n randomly chosen girls exceeds 150 n cm, for large n. marks
[2009/NYJC/II/6(modified)]
CJC · Review problems · Question 7
Use the 30 th and 70 th percentiles for a symmetric central 40% interval.