Answer:
Step-by-step explanation:
Given that that (X) the amount of time lapsed between consecutive trades on the New York Stock Exchange followed a normal distribution with a mean of 15 seconds.
i.e. X is normal with mean = 15 and unknown std deviation [tex]\sigma[/tex]
Given that[tex]P(X<13) = 7% = 0.07[/tex]
i.e. P([tex]z<\frac{13-15}{\sigma} )=0.07[/tex]
z=-1.475 (from normal table)
Hence [tex]\frac{13-15}{\sigma}=-1.475\\\sigma = 1.356[/tex]
Using this we find P(X>17) = [tex]P(Z>\frac{17-15}{1.356} \\=P(Z>1.475)\\=0.5-0.428\\=0.072[/tex]