SOLUTION: Pa got in his 29 Ford instead of driving west from Jackson is a constant speed of 30 mph. An hour later mom got in her 31 Buick and started driving west from Jackson at a constant

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Question 883180: Pa got in his 29 Ford instead of driving west from Jackson is a constant speed of 30 mph. An hour later mom got in her 31 Buick and started driving west from Jackson at a constant speed. After driving four hours ma had passed pa and was 10 miles ahead of him. How fast with ma driving
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Ma has to drive faster, or else she
can't catch Pa
Pa's speed = +30+ mi/hr
Let Ma's speed = +30+%2B+s+ mi/hr
--------------------------------
How much of a head start does Pa get?
+d%5B1%5D+=+30%2A1+
+d%5B1%5D+=+30+ mi
------------------
Start a stop watch when Ma leaves
Let +d+ = the distance Ma has traveled
when she catches Pa
Let +s+ = Ma's speed in mi/hr
-----------------------------
Pa's equation:
(1) +d+-+30+%2B+10+=+30%2A4+
Ma's equation:
(2) +d+%2B+10+=+s%2A4+
--------------------
(1) +d+-+20+=+120+
(1) +d+=+140+
Substitute this value into (2)
(2) +140+%2B+10+=+4s+
(2) +4s+=+150+
(2) +s+=+37.5+
-----------------
Ma is driving 37.5 mi/hr
check:
(2) +d+%2B+10+=+s%2A4+
(2) +140+%2B+10+=+37.5%2A4+
(2) +150+=+150+
OK