Question 242866
Well we know that distance/time = speed. 

So the duck's OWN speed (if flying without any wind) with the wind behind him is:

{{{(2400/10)-x/10}}} Where x/10 is the wind speed

The duck's OWN speed (if flying without any wind) with the wind against him is:

{{{(1600/10)+x/10}}} Where x/10 is the wind speed Remember {{{1600=2/3*2400}}}

So we have two equations that must equal each other since they both represent the duck's speed.

{{{(2400/10)-x/10 = (1600/10)+x/10}}} We need to rearrange to find x

{{{(2400/10)-x/10 = (1600/10)+x/10}}} Add x/10 to both sides and subtract (1600/10 from both sides gives:

{{{(2400/10)-(1600/10) = 2x/10}}}
{{{(800/10) = 2x/10}}}

so x must be 400/10 which 40 metres per minute.