Math Help Forum - View Single Post

WillB · #3 June 30th, 2009, 01:38 PM

I'm sorry. I am using tables to find the values. This is my first post and I am not really sure how this works. I will show you what I did so far.

a.

$P(\frac{75-80}{15}\le\frac{x-80}{\sqrt{225}}\le\frac{85-80}{15})=\Phi(0.3)-\Phi(-0.3)=0.6293-0.3707=0.2586$

b. P(X<50)

$\frac{50-80}{15}=-2$

$\Phi 2=0.9772$ (I'm not sure which table to use for >)

1-0.9772=0.0228

c. P(X>95)

$\frac{95-80}{15}=0.33333$

$1-\Phi 0.33333=1-0.6293=0.3707$

d. P(|X-80|>18)

I'm not exactly sure how you did it, but going from your work:
2(1-P(X<98)

$\frac{98-80}{15}=1.2$

$\Phi 1.2=0.8849$

2(1-0.8849)=0.2302