An old lady taking her elephant for a walk beside the river was dismayed to see it
falling over the steep, slippery bank towards
the water. Luckily it was harnessed to a
strong rope, and the lady managed to take
several complete turns of the rope around a
tree and hold on tightly enough to keep it
from the waiting crocodiles.
Each turn of the rope around the tree reduced the pull by 70%. Given that
the old lady, who is really quite strong, can support a weight of at most
50kg, while her elephant weighs 1 tonne, find the smallest number of
complete turns which the old lady could have used.
If she had used half a turn less could she still have held the elephant?