SOLUTION: "nancy and mark commute to work, traveling in opposite directions. Nancy leaves the house at 7am and averages 30 mph. mark leaves at 7:15 and averages 40 mph. at what time will th

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: "nancy and mark commute to work, traveling in opposite directions. Nancy leaves the house at 7am and averages 30 mph. mark leaves at 7:15 and averages 40 mph. at what time will th      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


   



Question 729735: "nancy and mark commute to work, traveling in opposite directions. Nancy leaves the house at 7am and averages 30 mph. mark leaves at 7:15 and averages 40 mph. at what time will they be 165 miles apart".
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Nancy has +1%2F4+ hr head start.
+d%5B1%5D+=+30%2A%281%2F4%29+=+7.5+ mi is her head start
Start a stopwatch when Mark leaves and stop
it when they are +165+ mi apart.
------------------------------
Let +t+ = the time on the stopwatch when stopped
Let +d+ = distance in miles Nancy travels in time +t+
+165+-+%28+d+%2B+7.5+%29+ = distance in miles Mark travels in time +t+
------------------------------
Nancy's equation:
(1) +d+=++30t+
Mark's equation:
(2) +165+-+%28+d+%2B+7.5+%29+=+40t+
---------------------------
(2) +165+-+d+-+7.5+=+40t+
(2) +d+%2B+40t+=+157.5+
Substitute (1) into (2)
(2) +30t+%2B+40t+=+157.5+
(2) +70t+=+157.5+
(2) +t+=+2.25+
7:15 AM + 2.25 hrs = 9:40 AM
They are 165 mi apart at 9:40 AM
check:
(1) +d+=++30t+
(1) +d+=++30%2A2.25+
(1) +d+=+67.5+
---------------
(2) +165+-+%28+d+%2B+7.5+%29+=+40t+
(2) +165+-+%28+d+%2B+7.5+%29+=+40%2A2.25+
(2) +165+-+7.5+-+d+=+90+
(2) +d+=+165+-+97.5+
(2) +d+=+67.5+
OK