(1)(100+x)÷25=5,
(100+x)÷25×25=5×25,
100+x=125,
100+x-100=125-100,
x=25;
(2)(1+80%)x=360,
1.8x=360,
1.8x÷1.8=360÷1.8,
x=200;
(3)1-25%x=
,1 4
1-0.25x=0.25,
1-0.25x+0.25x=0.25+0.25x,
0.25+0.25x=1,
0.25+0.25x-0.25=1-0.25,
0.25x=0.75,
0.25x÷0.25=0.75÷0.25,
x=3.