Răspuns:
30 min
inca 5min
GREAAAAAAAA!!!!
Explicație pas cu pas:
deci dupa 10min mariu a umplut (1/2)*(10/20) =1/4 butoi
andrei ramane singur as umple 3/4 butoi pecare singur l-ar fi unplut in 2*20=40 min
deci (3/4) il va umple4 in (3/4) *40=30 min
duopa inca 20 min. Anfrei umple inca 1/2 butoi
deci r5amane 1=1/4-1/2=1/4 butoi
pecatre cei 2 baieti il vor umple in 20*1/4 =5 min