=(31+1/3)*(41+1/2)-(11+1/3)*(41+1/2)-(11+1/3)*(41+1/2)-(9+1/2)*(11+1/3)
=[(31+1/3)-(11+1/3)]*(41+1/2)-[(41+1/2)+(9+1/2)]*(11+1/3)
=20*(41+1/2)-51*(11+1/3)
=820+10-561-17=252