4) 5/18=0.2777777778=0.28

5)

а) (3-15/28×7/6)×40/19=

=(3-5/4×1/2)×40/19=

=(3-5/8)×40/19=

=(24/8-5/8)×40/19=

=19/8×40/19=

=1/1×5/1=

=5

б) (92/27-53/18)÷50/27+18/5×1/3=

=(184/54-159/54)÷50/27+6/5×1/1=

=25/54×27/50+6/5=

=1/6×3/2+6/5=

=1/2×1/2+6/5=

=1/4+6/5=

=5/20+24/20=

=29/20=

=145/100=

=1.45