Fred walked 10 meters down and 24 to the right. You can think of these two segments as the legs of a right triangle.
The hypotenuse of this triangle is the path Fred would have walked through the pond. So, this distance is
[tex]d=\sqrt{10^2+24^2}=\sqrt{100+576}=\sqrt{676}=26[/tex]
So, instead of walking 10+24=34 meters, he could have walked 26 meters, saving 34-26=8 meters.