Question

A duck can fly 2400 m in 10 minutes with the wind. Against the wind, it can fly only 2/3 of this distance in 10 minutes. What is the rate of the wind?

Answer 1

The rate (or speed) of the wind is 40 meters per minute.

Explanation:

Let's define:

S = speed (or rate) of the duck alone

S' = speed (or rate) of the wind.

When the duck travels with the wind, its speed is:

(S + S')

While when the duck travels against the wind, its speed is:

(S - S')

Also, remember the relation:

Distance = Speed*Time

ok, we know that the duck can travel a distance of 2400 m in 10 minutes with the wind, then:

2400m = (S + S')*10 min

And against the wind, it can travel 2/3 of that distance, then we can write:

(2/3)*2400m = (S - S')*10 min

Then we have a system of 2 equations:

2400m = (S + S')*10 min

(2/3)*2400m = (S - S')*10 min

We want to find the speed of the wind, then we want to find the value of S'.

To solve this, we first need to isolate S in one of the equations.

Let's isolate S in the first one:

2400m = (S + S')*10 min

2400m/10min = (S + S')

240 m/min = S + S'

240 m/min - S' = S

Now we can replace this in the other equation:

(2/3)*2400m = (S - S')*10 min

(2/3)*2400m = ( 240 m/min - S' - S')*10 min

Now let's solve this for S'

(2/3)*2400m/10min = 240 m/min - 2*S'

(2/3)*240 m/min = 240 m/min - 2*S'

2*S' = 240 m/min - (2/3)*240 m/min

2*S' = (1/3)*240 m/min

2*S' = 80 m/min

S' = (80 m/min)/2

S' = 40 m/min

The rate (or speed) of the wind is 40 meters per minute.