31 1/3*41 1/2 -11 1/3*41 1/2*2-9 1/2*11 1/3
=94/3*83/2-34/3*83/2*2-19/2*34/3
=1/6(94*83-34*83-34*83-19*34)
=1/6[83*(94-34)-34*(83+19)]
=1/6(83*60)-1/6(34*102)
=83*10-34*17=830-578=252