6/25 :x=50
50x=6/25
50x=0.24
x=0.24/50
x=0.0048
1/4 x 1/5 x*45=12
1/4 x 1/5 x=12/45
(1/4加1/5)x=4/15
9/20 x=4/15
x=4/15 / 9/20
x=4/15 * 20/9
x=16/27