1.3/13-2/5+10/13-3/5
=(3+10)/13-(2+3)/5
=1-1
=0
2.2/7除以[3/7x(2/3+7/9)]
=(2/7)除以[3/7x(6/9+7/9)]
=(2/7)除以[3/7x(13/9)]
=(2/7)除以[13/21]
=(2x21)/(7x13)
=6/13