A=42 x91+6x19x7-420=42x91+(6x7)x19-42x10=42x(91+19-10)=42x(110-10)=42x100=4200
Tinh nhanh 1 } 42 x 91 + 6 x 19 x 7 - 4202 ) 99 x 1001 - 99
1) 42 x 91 + 6 x 19 x 7 - 420
= 42 x 91 + 6 x 7 x 19 - 42 x 10
= 42 x 91 + 42 x 19 - 42 x 10
= 42 x ( 91 + 19 - 10 )
= 42 x 100
= 4200
2) 99 x 1001 - 99
= 99 x ( 1001 - 1 )
= 99 x 1000
= 99000
1) 42 x 91 + 6 x 19 x7 - 420
= 42 x 91 + 42 x 19 - 420
= 42 x ( 91 + 19) - 420
= 42 x 100 - 420
= 4200 - 420
= 3780
2) 99 x 1001 - 99
= 99 x 1000 + 99 -99
= 99000 + 0
= 99000
Đúng chưa?
1 : 3780 hoặc 4200
2 : 99000
Đúng nha Nguyễn Như Quỳnh
99x1001-99=99x1001-99x1=99x(1001-1)=99x1000=99000
