(1)90×30=2700 500×50=25000 13×60=780 250×40=10000
(2)90÷3=30 4200÷7=600 9000÷6=1500 240÷6=40
(3)81÷4≈20 418÷7≈60 179÷6≈30 322÷4≈80
(4)31×49≈1500 89×40≈3600 52×68≈3500 43×21≈800
故答案为:2700,25000,780,10000,30,600,1500,40,20,60,30,80,1500,3600,3500,800.
(1)90×30=2700 500×50=25000 13×60=780 250×40=10000
(2)90÷3=30 4200÷7=600 9000÷6=1500 240÷6=40
(3)81÷4≈20 418÷7≈60 179÷6≈30 322÷4≈80
(4)31×49≈1500 89×40≈3600 52×68≈3500 43×21≈800
故答案为:2700,25000,780,10000,30,600,1500,40,20,60,30,80,1500,3600,3500,800.