SOLUTION: Please help me solve THIS problem. A car travels 840 mi. A second car traveling 2 mph faster than the first car, makes the same trip in 1 h less time. Find the speed of each ca

Question 736946:
Please help me solve THIS problem. A car travels 840 mi. A second car traveling 2 mph faster than the first car, makes the same trip in 1 h less time. Find the speed of each car. Thank You
Answer by checkley79(3341) (Show Source): You can put this solution on YOUR website!
D=RT
840=RT
R=840/T
840=(R+2)(T-1)
840=(840/T+2)(T-1)
840=840+2T-840/T-2
840-840=2T-840/T-2
0=(2T*T-840-2T)/T CROSS MULTIPLY:
2T^2-840-2T=0
2(T^2-T-420)=0
2(T-21)(T+20=0
T-21=0
T=21 HOURS ANS.
840=R*21
R=840/21
R=40 MPH.
PROOF:
840=(40+2)(21-1)
840=42*20
840=840

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