计算题.（1）5/18*1/4*90% 4/8/5-40% (5/8+5/6)*4/25 （2）8/5x-120%=5.

（1）5/18*1/4*90%
=5/18×1/4×9/10
=1/16
4/8/5-40%
=4/8×1/5-2/5
=1/10-4/10
=-3/10
(5/8+5/6)*4/25
=5/8×4/25+5/6×4/25
=1/10+2/15
=3/30+4/30
=7/30
（2）8/5x-120%=5.2
1.6x-1.2=5.2
1.6x=6.4
x=4
3x+90%*4=9
3x+3.6=9
3x=5.4
x=1.8
x-20%x=8
x-0.2x=8
0.8x=8
x=10