Counting the number of apples in a box is easy, one, two, three, four? and so on. Therefore some people might think that counting numbers is easy. But when the number gets big, you can?t do it like the way you count the apples.

Take for an example counting the number of trees on a mountain. If it is a big mountain, its hard to count alone. You need to find more peoples, assign them to different sectors. However, there will be errors of repeated count or miscount. So how do you count the exact correct number of trees ?

The most easy way is to mark on the trees to avoid repeated count. But marking on trees have some disadvantages. First, how do you assure that no trees are left out? Marking on trees could avoid repeated counts, but could not avoid miscount. Moreover, doing marks on trees will lower the value of the trees. Besides that, even if all the peoples pay their full attention on counting the trees, there might be one or two of them does some mistakes. So, how to count the trees correctly? Before scrolling down, think about it for a moment.

 

 

 

 

 

 

 

 

 

 

 

 

 

First, take a guess of the number of trees on the mountain. Prepare some ropes to tie on the trees. Then distribute the ropes to each people, and each of them need to tie those ropes on the trees.

When all the trees are tied, use the number of prepared ropes, minus the number of trees left untied, and you will get the answer !

For example if you prepared 10,000 ropes, and there are 3500 ropes left, then the number of trees will be:

10,000 - 3500 = 6500 trees