The distance from Adelaide to Stansbury by road is how many miles longer than the distance from Adelaide to Stansbury by sea?
(1) If a car and a boat left Adelaide at the same time and both traveled at an average speed of 30 miles per hour, the boat would arrive at Stansbury 3 hours before the car.
(2) If a car traveled at an average speed of 60 miles per hour and a boat traveled at an average speed of 15 miles per hour, each would complete the trip from Adelaide to Stansbury in 2 hours.
Source: kaplan
The distance from Adelaide to Stansbury by road is how many
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Let's say the car's rate = c, the car's time = d, the boat's rate = b, and the boat's time = a.
From that, we have
Car's Distance = cd
Boat's Distance = ab
and we want |cd - ab|.
S1
30*d = 30*(a - 3)
30d = 30a - 90
d = a - 3
c = 30
b = 30
so
|cd - ab| => |30*(a - 3) - 30*a| => |30a - 90 - 30a| => 90; SUFFICIENT.
You can also see this conceptually by imagining each vehicle. When the boat completes the journey, it and the car have traveled the SAME mileage, since they've each gone for x hours @ 30 mph. At that point, the car has to make up the remaining distance. It takes 3 hours @ 30 mph to do so, so the car travels an extra 90 miles, making the car's distance 90 miles longer.
S2
60*2 = 15*2
This tells us the distance for each: the car has to travel 120 miles (60 mph * 2 hours) and the boat has to travel 30 miles (15 mph * 2 hours). So we have each distance, and can find the different: 120 - 30; SUFFICIENT.
From that, we have
Car's Distance = cd
Boat's Distance = ab
and we want |cd - ab|.
S1
30*d = 30*(a - 3)
30d = 30a - 90
d = a - 3
c = 30
b = 30
so
|cd - ab| => |30*(a - 3) - 30*a| => |30a - 90 - 30a| => 90; SUFFICIENT.
You can also see this conceptually by imagining each vehicle. When the boat completes the journey, it and the car have traveled the SAME mileage, since they've each gone for x hours @ 30 mph. At that point, the car has to make up the remaining distance. It takes 3 hours @ 30 mph to do so, so the car travels an extra 90 miles, making the car's distance 90 miles longer.
S2
60*2 = 15*2
This tells us the distance for each: the car has to travel 120 miles (60 mph * 2 hours) and the boat has to travel 30 miles (15 mph * 2 hours). So we have each distance, and can find the different: 120 - 30; SUFFICIENT.