Răspuns:
Explicație pas cu pas:
S = suma de bani primita de Mihai
Prima cheltuiala 2S/5
Rest S - 2S/5 = 5S/5 - 2S/5 = 3S/5
A doua cheltuiala (25% = 25/100 = 1/4)
1/4 x 3S/5 = 3S/20
Rest 3S/5 - 3S/20 = 12S/20 - 3S/20 = 9S/20
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9S/20 = 54 lei
S = 20*54/9 = 120 lei