简算20-1/4×2/5 5/6（7/16+4/5）÷3/5 18/25×9/10+7

20-1/4×2/5×5/6
=20-1/10×5/6
=20-1/12
=19又12分之11；
（7/16+4/5）÷3/5
=(7/16+4/5)×5/3
=35/48+4/3
=(35+64)/48
=99/48
=33/16;
18/25×9/10+7/25×9/10+9/10
=9/10×(18/25+7/25+1)
=9/10×2
=9/5;
解方程x-3/8x=5/10
5x/8=5/10;
x=4/5;
9x÷1/2=2/9
9x×2=2/9;
x=1/81;
x×(1-2/5)=48
3x/5=48;
x=80;