Notam suma initiala cu x.
In prima luna a scos x/2
Dupa prima luna a mai avut x-x/2 = 2x/2-x/2 = x/2
In a doua luna a scos x/2 * 1/3 = x/6
Dupa a doua luna mai are x/2-x/6 = 3x/6-x/6 = 2x/6 = x/3
In a treia luna a scos x/3 * 1/2 = x/6
Dupa a treia luna mai are x/3-x/6 = 2x/6-x/6 = x/6
In a patra luna a scos x/6*1/3 = x/18
Dupa a patra luna mai are x/6-x/18 = 3x/18-x/18 = 2x/18 = x/9
Aceasta suma reprezinta 240 euro, adica:
x/9 = 240
x = 240*9
x = 2160 euro a avut initial in cont