x/2-x/5=90
解:1/2x-1/5x=90
3/10 x=90
x=90×10/3
x=300
选我吧?!
先通分,再解
得x=300
解: 1 1
-X - -X=90
2 5
X=300
解:(1/2-1/5)x=90
3/10x=90
x=90x10/3
x=300
x/2-x/5=90
解:1/2x-1/5x=90
3/10 x=90
x=90×10/3
x=300
x/2-x/5=90
5x/10-2x/10=90
3x/10=90
x=300