Răspuns:
Explicație pas cu pas:
25% = 25/100 = 1/4
20% = 20/100 = 1/5
S = suma initiala
a cheltuit 25%, adica S*1/4
rest S - S/4 = 3S/4
a mai cheltuit 20% din rest, adica 3S/4*1/5 = 3S/20
rest 3S/4 - 3S/20 = 15S/20 - 3S/20 = 12S/20 = 3S/5
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3S/5 = 252 lei
S = 252*5/3 = 420 lei