Question

Darrin can skateboard 2 miles against a 4 mph wind in the same amount of time he skateboards 6 miles with a 4 mph wind. Find the speed Darrin skateboards with no wind.

Answer 1

Speed without wind will be 8 mph

Explanation:

Now by revising basic formula here

Velocity = Distance/Time. . . . (A)

Assume speed without wind is 'x'

When Darrin is moving against wind to cover 2 miles;

net speed will be x-4

When Darrin is moving along with the wind to cover 6 miles;

net speed will be x+4

Please note that the time for covering distance of 2 miles and 6 miles is same,

So, from equation (A)

Time = Distance/Velocity,

Time for 2 miles will be

Time = 2/(x-4)

Time for 6 miles will be

Time = 6/(x+4)

Since, the time for both distances is same, here we can equate,

2/(x-4) = 6/(x+4)

by cross multiply

2(x+4) = 6(x-4)

2x+8 = 6x-24

4x = 32

x = 8

So, 8 miles per hour is the speed of Darrin if there is no wind.

Answer 2

Speed = 8mph

Explanation:

Speed of wind = 4mph

Let speed of Darrin with no wind be "x" mph

then resultant speed of Darrin, travelling in direction of wind = (x + 4) mph

Using a result, Time = Distance travelled / Net speed

Time taken by Darrin to travel 6miles in direction of wind = 6 / (x + 4)

When Darrin travel in opposite direction of wind, then its net speed = (x - 4)mph

Darrin travel 2 miles against the wind in 6/(x + 4) hr

then Distance = speed × time

2 = ( x- 4 ) × ( 6/x + 4)

2x + 8 = 6x - 24

4x = 32

x = 8 mph

Therefore speed of Darrin skateboard with no wind = 8mph