The situation of theRiddle of the lake nymphs It is this: in a lake there is a water lilies. This plant grows at a precise speed: every day the patch formed by its Leaves doubled of size. This means that – if we take it for granted that the size of the leaves is always the same – if the first day there is only one leaf, the second day there will be two, the third four leaves, the fourth eight, and so on … the question is now this: if they love us 72 days For Fill the whole lake of leaves, how many days did it take for fill it in half?
A common response that is given to this riddle is half of the days, in this case 36. But … it’s wrong! It would be right if, every day, the leaves grew the same quantity, while in our case they double! The right answer is another.
If in 72 days The lake fills completely and every day doubles the number of leaves, it means that al 71or day There are exactly half of the leaves of day 72! And therefore the answer is just 71 If we want to mathematically describe this problem, we can describe it with the equation y(x) = 2x, Where x It is the day considered e y(x) is the amount of leaves a day x.
This type of riddle, in addition to delighting us, are very useful above all for the little ones to learn rules and mathematical formulas that may seem difficult, but which, seen through a simple example such as that of the lake and water lilies, become easy and intuitive. Another famous example of explanation of exponential growth and of the doubled power It is the legend of the birth of the chess, in which the inventor of the chess as a reward for his splendid invention, asked that he would be given a grain of rice for the first box, two for the second, four for the third, eight for the fourth and so on, a number of double rice beans for each of the 64 chess boxes. The result was that his reward amounted to 18 billion billions of rice beans!
