a) 98 + 3 + 97 +2
= (98 +2) + ( 97 + 3)
= 100 + 100 = 200
56 + 399 + 1 + 4
= (56 + 4) +( 399 + 1)
= 60 + 400 = 460
b) 364 + 136 + 219 + 181
= (364 + 136) + (219 + 181
= 500 + 400 = 900
178 277 + 123 + 422
= (178 + 422) + (277 + 123)
= 600 + 400 = 1000
tính bang cach thuyen tien nhat;236+400+364=.......