s= suma initiala
cat a cheltuit in prima zi=s/3+20, cat a ramas dupa prima zi=s-s/3-20=2s/3-20
cat a cheltuit a doua zi=(2s/3-20)x(40/100)=(2s/3-20)x(2/5)=4s/15-40/5=4s/15-8
s=s/3+20+4s/15-8+60, numitor comun=15
15s=5s+300+4s-120+900, 15s-9s=1200-120, 6s=1080, s=1080/6=180 lei
