1:6分之5*13分之1+9分之5*13分之2+18分之5*13分之6
=5/6x1/13+10/9x1/13+5/3x1/13
=(5/6+10/9+5/3)x1/13
=65/18x1/13
=5/18
2:9分之5*79又17分之16+50*9分之1+9分之1*17分之5
=5/9x79又16/17+5/9x10+5/9x1/17)
=5/9x(79又16/17+10+1/17)
=5/9x90
=50
3:15分之7*8分之3+15分之1*16分之7+15分之1*3又2分之1
=7/15x3/8+7/15x1/16+7/15x1/2
=7/15x(3/8+1/16+1/2)
=7/15x15/16
=7/16