SOLUTION: 1 car travels 15 miles an hour the 2nd car travels 30 miles an hour. The first car traveling at 15 miles an hour gets a 20 second head start. Which car will be the first to cross

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Question 943456: 1 car travels 15 miles an hour the 2nd car travels 30 miles an hour. The first car traveling at 15 miles an hour gets a 20 second head start. Which car will be the first to cross the finish line which is .25 miles away? What is the formula used in this math problem?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
How much of a head start did the 1st car get?
You have to convert +20+ sec to hours
( seconds ) x ( minutes / second ) x ( hours / minute ) = hours
+20%2A%28+1%2F60+%29%2A%28+1%2F60+%29+=+20%2F3600+
+20%2F3600+=+1%2F180+ hrs
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Let +d%5B1%5D+ = 1st car's head start in miles
+d%5B1%5D+=+r%2At+
+d%5B1%5D+=+15%2A%28+1%2F180+%29+
+d%5B1%5D+=+5%2F60+
+d%5B1%5D+=+1%2F12+ mi
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If you start 2 stopwatches when the 2nd car leaves,
and you time both cars, then you let +t%5B1%5D+ =
1st car's time in hrs, and +t%5B2%5D+ = 2nd car's
time in hrs
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2nd car's equation:
+1%2F4+=+30t%5B2%5D+
+t%5B2%5D+=+1%2F120+ hrs
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1st car's equation:
+1%2F4+-+1%2F12++=+15t%5B1%5D+
+3%2F12+-+1%2F12+=+15t%5B1%5D+
+15t%5B1%5D+=+1%2F6+
+t%5B1%5D+=+1%2F90+ hrs
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+1%2F120+ is smaller than +1%2F90+, so
the 2nd car crosses first