{2.74-0.56*(2又5/12-1又19/60+2.275)}*1又3/17
={2.74-0.56*(1.1+2.275)}*1又3/17
={2.74-0.56*3.375}*1又3/17
={2.74-1.89}*1又3/17
=0.85*20/17
=1