SOLUTION: Carol drove for 3 hours on a two lane state road she then increased her speed by 10 miles per hour on the freeway and drove for 6 more hours if the total trip was 555 miles then

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Question 675157: Carol drove for 3 hours on a two lane state road
she then increased her speed by 10 miles per hour on the freeway and drove for 6 more hours
if the total trip was 555 miles then what was her speed on the freeway

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +s+ = her speed on the 2 lane state road in mi/hr
Let +d+ = her distance on the state road in miles
+s+%2B+10+ = her speed on the freeway in mi/hr
+555+-+d+ = her distance on the freeway in miles
-----------
Equation for state road:
(1) +d+=+s%2A3+
Equation for freeway:
(2) +555+-+d+=+%28+s+%2B+10+%29%2A6+
--------------------------
Substitute (1) into (2)
(2) +555+-+3s+=+%28+s+%2B+10+%29%2A6+
(2) +555+-+3s+=+6s+%2B+60+
(2) +9s+=+555+-+60+
(2) +9s+=+495+
(2) +s+=+55+
+s+%2B+10+=+65+
Her speed on the freeway was 65 mi/hr
check:
(1) +d+=+s%2A3+
(1) +d+=+55%2A3+
(1) +d+=+165+
and
(2) +555+-+d+=+%28+55+%2B+10+%29%2A6+
(2) +555+-+d+=+65%2A6+
(2) +d+=+555+-+390+
(2) +d+=+165+
OK