Fie x suma initiala.
In prima zi elevul a cheltuit 1/3x si a ramas cu x - 1/3x = 2/3x
A doua zi:
25/100 * (2/3)x = 1/4 * 2/3 *x = 1/6 x
Deci a ramas cu 2/3 x - 1/6 x = (4/6 - 1/6)x = 3/6 x = 1/2 x
A treia zi a cheltuit: 2* 1/6 x = 1/3 x
A ramas cu :
1/2 x - 1/3x = 1/6 x
Acest rest este efal cu 100:
(1/6) * x = 100
x = 600 lei