X×(1-2/5)+(72-X)×(1-5/9)=39

问题描述:

X×(1-2/5)+(72-X)×(1-5/9)=39

X×(1-2/5)+(72-X)×(1-5/9)=39
3/5X+32-4/9X=39
3/5X-4/9X=39-32
7/45X=7
X=7÷7/45
X=45