my question in regards to funding the proportion through z scores.

the question is asking to

5. 15 An investigator polls common cold sufferers, asking them to estimate the number of hours of physical discomfort caused by their most recent colds. Assume that their estimates approximate a normal curve with a mean of 83 hours and a standard deviation of 20 hours. 

and I am needing to figure out

(b) What proportion of sufferers estimate that their colds lasted longer than 48 hours? 

I understand that I need to convert X (48 hours) into a z score in which I figured out I got a z score of -1.75

then my text book shows I need to minus this answer by 1 (z score) which gives me an answer of 0.95…

P(z> -1.75) = 1-0.0401

= .9599

= 95.99%

I’m unsure why we are misusing this by 1??