Probability of sample - getting Too large a Z value

[cadag]

I'm working on this more advanced problem:

Population proportion of college students that attend every class is 0.15
What is the probability that out of 100 students sampled, the proportion of those attending every class is between 0.1 and 0.3?

I thought I knew how to solve this, but I keep getting a Z value greater than 3, which is too big to be listed in the Z table that we use. This is what I did:

Use Infinite population formula for Standard deviation(SD) of P:

SD[of P] = SQRT(P(1-P)/n))

so thats: SQRT(0.15(1-0.15)/100)) which = 0.0358

Then using the Z formula which is:

Z = (X[value your using] - Population Proportion)/ SD[of p]

so thats Z = ((0.3-0.15)/0.0358) = 4.1899

right here I'm getting a Z value of 4+, which is too big to use in the Z tables. However the calculations for the 0.1 area works out ok to a Z value of -1.39, but I' not sure how to find the area of the .3, since the Z value is too big for the table. Any help is greatly appreciated.

Basically My idea to solve it is to just substract the 0.1 area from the 0.3 area, which will give me the area between 0.1 and 0.3 which will be the probability that it is between 0.1 and 0.3

 

[royhaas]

Use a probability of 1 for the large z-value. Subtract the probability for the z-value corresponding to 0.1.

 

[cadag]

thanks, that make sense