A/B ==2/5,
B/C ==5/3,
A+B+C==60, solve for A, B, C
A==12 kg, B==30 kg, C==18 kg
Grade B==7/kg
Grade A==7/kg - 2==5/kg
Grade C==7/kg + 3==10/kg
B==7/kg x 30 kg==210 - Grade B pears
A==5/kg x 12 kg ==60 - Grade A pears
C==10/kg x 18 kg==180 Grade C pears
So: A : B : C ==60 : 210: 180==2 : 7 : 6 [Their ratio by the number of pears in all 3 grades]
