Normal distribution and SD Simple question

[dbuk2000]

T is the waiting time in seconds for a customer care representative of TechCo to respond to a customer's first question in an online chat session. You are given that T~ N( 19.1, 3^2). Find: P(T< 17)

Can anyone help. I put into my TI-84 calculator the normalCDF(0,16,19.1,3) but get nowhere near the answer which is 0.0620.

Where am I going wrong?

 

[Dr.Peterson]

T is the waiting time in seconds for a customer care representative of TechCo to respond to a customer's first question in an online chat session. You are given that T~ N( 19.1, 3^2). Find: P(T< 17)

Can anyone help. I put into my TI-84 calculator the normalCDF(0,16,19.1,3) but get nowhere near the answer which is 0.0620.

Where am I going wrong?

Why did you enter 0, 16? That would find the probability from 0 to 16, not from negative infinity to 17.

 

[dbuk2000]

I thought at the lowest waiting time is 0 but actually I've tried many different combinations. Using -9999 as the minimum and 17 as the maximum but I can't seem to get close to the answer. Hoping someone can let me know what I need to input?

 

[Dr.Peterson]

I thought at the lowest waiting time is 0 but actually I've tried many different combinations. Using -9999 as the minimum and 17 as the maximum but I can't seem to get close to the answer. Hoping someone can let me know what I need to input?

Because the normal distribution extends to negative numbers, we don't want to exclude them; but that won't make a significant difference. The important part was your use of 16 rather than 17. I was wondering if you were trying to make a continuity correction (which is probably not appropriate here, and 16 would be wrong anyway).

I don't have a (working) TI-84, but using Excel I, too, can't get near the claimed answer. I get 0.241964, and would guess that their answer is an error. (If you had told me what number you got, I would have more quickly checked the answer!)