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2supra31+4supra21+1supra41

Răspuns :

2/31+4/21+1/41=(2*21*41+4*31*41+31*21)/31*21*41=
=(1722+5084+651)/26691=7457/26691

a=nr baieti
20%a=20a/100=a/5=nr fete
a+a/5=30
5a+a=150
6a=150
a=25 baieti
a/5=25/5=5 fete