Probability question

[ReganM]

I found this question on the iTutes forum (copied):
http://www.itute.com/board/viewtopic.php?f=2&t=1441

The newspaper will be sent to you between 6:30 and 7:30 am every day. And you will leave for school between 7:00 to 8:00 every morning. What's the probability that you can get the newspaper before you leave?


(The correct answer is P(get the newspaper before leaving)=0.875)
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And an explanation of the answer is posted below it, but I don't get how they got the answer. I don't even understand the diagram, heh. I get the t=.5,1 etc. But shouldn't the graph 'stop' at 7.30 because you would've left already? Also I don't get how they get p, and I'm assuming p is... chance of getting the newspaper?

thanks! I hope I'm not too confusing.

[mikee65]

they just want from 0 to 1 bc you leave at 1 first they need to find P in order to work it out. Nice Q btw

[ReganM]

huh. I'm still confused. How did they get the equation to find p? Where do all those values come from. o_O I know that when you want to find the area you can use 'area of shapes' to figure it out... but when I tried I didn't get the same answer.

..and how would you be able to find the Pr of getting the newspaper without a calculator?

@mikee65 : umm, thanks for posting. Sorry, I can't really understand your post! I know they want 0 to 1 but why doesn't the graph "stop" at 1? Because after that there is no chance of getting the newspaper...? I think.

EDIT:

okay, wait. so I think I get it now. This is a Pdf for STAYING AT HOME. OKAY. So like, probability of being at home to recieve the newspaper?

okay, i did it and got p=1. But umm... how about getting the probably without a calc?