1) 10×x=8×25
10×x=200
x=200÷10
x=20
2)x÷20=4800÷80
x÷20=60
x=20×60
x=1200
3)(x-380)×50=2000
x-380=2000÷50
x-380=40
x=380+40
x=420
4)(x+8)÷70=4
x+8=4×70
x+8=280
x=280-8
x=272
5)640÷(25-x)=40
25-x=640÷40
25-x=16
x=25+16
x=41
6)2700÷(x-12)=90
x-12=2700÷90
x-12=30
x=30+12
x=42