12/7-(1/3÷7/15+4/13)
=12/7-(1/3*15/7+4/13)
=12/7-(5/7+4/13)
=12/7-5/7-4/13
=1-4/13
=9/13
89*5/88
=(88+1)*5/88
=88*5/88+1*5/88
=5+5/88
=5又5/88
11/12*13-11/12
=11/12*(13-1)
=11/12*12
=11
(3/7-1/34)*7-27/34
=3/7*7-1/34*7-27/34
=3-7/34-27/34
=3-(7/34+27/34)
=3-1
=2