SOLUTION: I am not sure how to find either of the unknowns in this equation. Either that or I am missing something that is known. A bank robber robs a bank and speeds away on the freeway a

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Question 1861: I am not sure how to find either of the unknowns in this equation. Either that or I am missing something that is known. A bank robber robs a bank and speeds away on the freeway at 80 miles/hour. Thirty minutes later police officers take off in pursuit at 90 miles/hour. How long will the police have to drive to catch up and how far from the bank will they catch the robbers?
Answer by longjonsilver(2297) About Me  (Show Source):
You can put this solution on YOUR website!
this is fairly easy to be honest, just don't freak out at converting the english to maths...just take it steady...
Let r = speed of robber = 80mph
Using speed+=+distance%2Ftime, we get 80 = d/t....equation1
Let p = speed of police = 90mph. And note they start 30 minutes later (or 1/2 hours later!!!!!).
so, for the police to arrive at the same point (d miles), we have 90 = d%2F%28t-%281%2F2%29%29 equation2
Substitute equn1 into 2 for d ie d=80t. So equation2 is now
90+=+%2880t%29%2F%28t-%281%2F2%29%29
90%28t-%281%2F2%29%29+=+%2880t%29
90t+-+45+=+80t
10t+=+45
therefore t = 4.5 hours.
Hence, as d=80t, d=360miles.

cheers
Jon.