=-11又2/3除以2-【(-20又1/2)+10.5】/2=11又2/3除以2-5=5/6
(-11又2/3)除以2-(-20又1/2)除以2+10.5除以2 =1/2*[-(11+2/3)+(20+1/2)+10.5]=1/2*[-(11+2/3)+31]=1/2*[20-2/3]=10-1/3=9又2/3 .
