(1)125×36-3603.6+36
=125×36-360.36÷360×100
=125×4×9-100.1
=500×9-100.1
=4500-100.1
=4399.9
(2)8/25+x=x/2
16+50x=25x,
25x=-16
x=-16/25.
(3)1/12+1/20+1/30+1/56+1/72+1/90
=1/3×4+1/4×5+1/5×6+1/6×7+1/7×8+1/8×9+1/9×10
=(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+.+(1/9-1/10)
=1/3-1/10
=7/30 (裂项法)
设原来长x米,列方程:
x-x/3+24=(1+20%)x
10x+360=18x
18x-10x=360
8x=360
x=360÷8
x=45.