Source: GMAT Prep
Two dogsled teams raced across a 300-mile course in Wyoming. Team A finished the course in 3 fewer hours than team B. If team A's average speed was 5 mph greater than team B's, what was team B's average mph?
A. 12
B. 15
C. 18
D. 20
E. 25
The OA is D
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Two dogsled teams raced across a 300 mile course in Wyoming.
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BTGmoderatorLU
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B
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E
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Manasa3190
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Given,
Total distance = 300 miles
Let team B speed be X
then, Team A speed = X+5
Time B - Time A = 3 hours
(300/x) - (300/(x+5)) = 3
x^2 +5*x - 500 =0
x = 20, -25
Speed can only be positive, so Speed of B is 20
Total distance = 300 miles
Let team B speed be X
then, Team A speed = X+5
Time B - Time A = 3 hours
(300/x) - (300/(x+5)) = 3
x^2 +5*x - 500 =0
x = 20, -25
Speed can only be positive, so Speed of B is 20
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GMATGuruNY
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We can PLUG IN THE ANSWERS, which represent B's speed.BTGmoderatorLU wrote:Source: GMAT Prep
Two dogsled teams raced across a 300-mile course in Wyoming. Team A finished the course in 3 fewer hours than team B. If team A's average speed was 5 mph greater than team B's, what was team B's average mph?
A. 12
B. 15
C. 18
D. 20
E. 25
When the correct answer is plugged in, B's time - A's time = 3 hours.
For each team:
Time = distance/speed = 300/speed.
B: B's speed = 15 mph, implying that A's speed = 15+5 = 20 mph
In this case, B's time - A's time = 300/15 - 300/20 = 20 - 15 = 5 hours.
Eliminate B.
D: B's speed = 20 mph, implying that A's speed = 20+5 = 25 mph
In this case, B's time - A's time = 300/20 - 300/25 = 15 - 12 = 3 hours.
Success!
The correct answer is D.
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As a tutor, I don't simply teach you how I would approach problems.
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Let's let the rate of team B be r. The time of Team A is 300/(r + 5) and the time of team B is 300/r; thus:BTGmoderatorLU wrote:Source: GMAT Prep
Two dogsled teams raced across a 300-mile course in Wyoming. Team A finished the course in 3 fewer hours than team B. If team A's average speed was 5 mph greater than team B's, what was team B's average mph?
A. 12
B. 15
C. 18
D. 20
E. 25
The OA is D
300/(r + 5) + 3 = 300/r
Multiplying by r(r+5), we have:
300r + 3r^2 + 15r = 300r + 1500
3r^2 + 15r - 1500 = 0
r^2 + 5r - 500 = 0
(r + 25)(r - 20) = 0
r = -25 or r = 20
Since r can't be negative, team B's average speed is 20 mph.
Answer: D
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