x÷2-x÷5=90

x÷2-x÷5=90
=5X-2X=900
=3X=900
=X =300
或化成x(1/2 - 1/5))=90
或化成(5x-2x)/10=90来求
还可换元设x÷2等于Y得Y+2Y/5=90求出Y

原式两边同时乘以10得
5x - 2x = 900
3x = 900
x = 300

x÷2-x÷5=90
x/2-x/5=90
x(1/2 - 1/5))=90
x=90÷(0.5-0.2)=90÷0.3=300

x÷2-x÷5=90
x/2-x/5=90
5x/10-2x/10=90
(5x-2x)/10=90
5x-2x=90*10
3x=900
x=300

X/2＝X/5+90
(X/2)*10=(X/5)*10+900
5X=2X+900
3X=900
X=300