(I haven't included the main question as it isn't relevant, it's just giving some context about a guy who is travelling to his work that opens at 08:30am but he starts at 09:00am). I'll happily post it and the other question parts if anybody would like to see them. So I am a bit confused by the question and it's wording.
I didn't really know what it meant by 'maximise his chance of arriving between ...', I just assumed it meant the probability being as close to 1 as possible.
Therefore I found the z value for a p of 0.999, and then rearranged the formula
z=(x-mean)/standard deviation, to find the corresponding x value.
I got a value of 52.7 (53 minutes), so concluded that he has a 99.9% chance of arriving to work within 53 minutes, and I took that away from 09:00am (
I was unsure at this part, I just guessed it would be at 09:00am) to get a final answer of 08:07am.
This appears to be wrong though, so I'd love some advice on where I went wrong/how to approach it?