1>
a) 15.80+6-100
= 1200+6-100
= 1206-100
= 1106
b)2,3.90+88:8
= 270+11
=281
c)890.21:7-245
=18690:7-245
=2670-245
=2425
Câu 1: a) 15.80+6-100
=1200+6-100=1106
b) 2,3.90+88:8
=207+11=218
c) 890.21:7-245
= 2670-245=2425
Câu 1 : Tính
a;15.80+6-100=1200+6-100=1206-100=1106
b;2,3.90+88:8=207+88:8=207+11=218
c;890.21:7-245=18690:7-245=2670-245=2425
Câu 2 : Tính nhanh
a;99+98+97+......+3+2+1
=(99+1) x <(99-1):1+1> : 2
=100 x 99:2
=4950
b;23.(99+2)+23.(1+98)
=23.(99+2+1+98)
=23.200
=4600
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