20 : ( 7 - 3 1/4 )× 1 4/5 - 5 1/2 =

=20÷(6 4/4-3 1/4)×9/5-5 1/2=20÷3 3/4×9/5-5 1/2=20×4/15×9/5-5 1/2=48/5-5 1/2=5.6-5.5=0.1