SOLUTION: Jennifer traveled at a constant speed on an old road for 160 miles. She then traveled 5 miles per hour faster on a newer road for 90 miles. If she drove for 6 hours, find the car's

Question 146545: Jennifer traveled at a constant speed on an old road for 160 miles. She then traveled 5 miles per hour faster on a newer road for 90 miles. If she drove for 6 hours, find the car's speed for the part of the trip that was traveled on the new road.
While you might find the speed on the old road in your calculations, do not include that in your answer. Do not include units in your answer.
Answer by edjones(8007) (Show Source): You can put this solution on YOUR website!
Let old road speed be s, new road speed be s+5; d=160+90, t=6
d=ts
d/s=t
160/s + 90/(s+5)=6
160(s+5)+90s=6s(s+5) Multiply each side by the LCM to eliminate fractions.
160s+800+90s=6s^2+30s
6s^2+30s-160s-90s-800=0 Subtract the left side from the right.
6s^2-220s-800=0
2(3s^2-110s-400)=0
(s-40)(3s+10)=0 Factor (or use the quadratic formula)
s=40
s+5=45 mph answer
.
Ed
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