Solving a Probability Question with Griffith's Quantum Mechanics

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Hi there, math geeks. Physics geek here. I came across this problem in Griffith's Introduction to Quantum Mechanics, and just can't decide how to attack it.
A needle of length L is dropped randomly onto a sheet of paper ruled with parallel lines a distance L apart. What is the probability that the needle will cross a line?
I've done the previous problems, but this one just threw me for a loop. Can anyone give me some advice? Thanks!

- Warren
 
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Thanks for the tip, Ambitwistor!

- Warren
 

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