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car travels....

by shibal » Fri May 01, 2009 11:01 am
it takes car A to travel 400 miles 2 hours less than car B (same distance). if the avg of car A's speed was 10 miles per hour greater than that of car B, what was Car B's avg speed per mile?
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by dmateer25 » Fri May 01, 2009 11:27 am
…….Rate….Time….Distance
A…..R+10…..T-2…..400
B…..R……….T…….400


RT = RT +10T -2R – 20
2R + 20 = 10T
R+10 = 5T
(R+10)/5 = T


R(R+10)/5 = 400

R^2 + 10R = 2000

R^2 + 10R – 2000 = 0

(R + 50)(R – 40) = 0

R= -50 or R=40


R can’t be negative so R is 40.
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by maihuna » Fri May 01, 2009 11:36 am
it takes car A to travel 400 miles 2 hours less than car B (same distance). if the avg of car A's speed was 10 miles per hour greater than that of car B, what was Car B's avg speed per mile?

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400/B - 400/A =2 or 1/B - 1/A = 1/200
Given : A = B + 10
so 1/(B) - 1/B+10 = 1/200
(B+10 - B)/B(B+10) = 1/200
2000 = B(B+10) = 40*50
so B=40 mph

ans 40mph
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