a) 98 + 47 = (98 + 2) + (47-2)
= 100 + 45 = 145
b) 199 + 56 = (199 + 1) + (56 - 1)
= 200 + 55 = 255
c) 2997 + 113 = (2997 + 3) + (113 - 3)
= 3000 + 110 = 3110
d) 121 - 98 = (121 + 2) - (98 + 2)
= 123 - 100 = 23
e) 286 - 99 = (286 + 1) - (99 + 1)
= 287 - 100 = 87
f) 1213 - 997 = (1213 + 3) - (997 + 3)
= 1216 - 1000 = 216
g) 16 . 50 = (16 . 5) . (50 : 5)
= 80 . 10 = 800
h) 28 . 25 = (28 : 4) . (25 . 4)
= 7 . 100 = 700
i) 24 . 125 = (24 : 8) . (125 . 8)
= 3 . 1000 = 3000
k) 1300 : 50 = (1300 . 2) : (50 . 2)
= 2600 : 100 = 26
l) 600 : 25 = (600 . 4) : (25 . 4)
= 2400 : 100 = 24
Học tốt.