1)13цел4/13-2цел13/20=173/13-53/20=20×173--13×53/260=2771/260=10цел171/260

2)10цел171/260+9/13=2771/260+9/13=

2771+20×9/260=2951/260=227×

×13/20×13=11цел7/20