1ye =a, 2ye ravno a*40/100=2a/5 3ye budet= 2a/5*175/100=7a/10
to: sred arif= (a+2a/5+7a/10)/3= (10a+4a+7a)/30=21a/30=7a/10
otvet 7a/10
(ili: pervoye bukva pust budet 10 toqda vtoroye budet 10*40/100=4 a 3ye budet 4*175/100=7 i srednoye arf.= 10+4+7/3=7)