a) 217 x 11

= 217 x (10 +1)

= 217 x 10 + 217 x 1

= 2170 + 217 = 2387

217 x 9 = 217 x (10-1)

= 217 x 10 - 217 x 1

= 2170 - 217 = 1953

b) 413 x 21 = 413 x (20 + 1)

= 413 x 20 + 413 x 1 = 8673

413 x 19 = 413 x (20-1)

= 413 x 20 - 413 x 1 = 7847

c) 1234 x 31 = 1234 x (30 +1)

= 1234 x 30+ 1234 x 1

= 37020 + 1234 = 38254

875 x 29 = 875 x (30 -1)

= 875 x 30 - 875 x 1

= 26250 - 875 = 25375

217 x 45 + 50 x 217 + 217 x 5

= 217 x (45 + 50 + 5)

= 217 x 100

= 21 700

1. 2000/1000 = 2

a, 217 + [ 43 + ( - 217 ) + ( - 23 ) ]

= 217 + 43 - 217 - 23

= ( 217 - 217 ) + ( 43 - 23 )

= 0 + 20 = 20

b, 273 + ( -123 ) = 273 - 123

                           = 150

c, 1 + ( -3 ) + ( -5 ) + (- 7 ) + ( - 11 )

= [ 1 + ( -11 ) ] + [ ( -3 ) + ( -7 ) ] + ( - 5 )

= ( -10 ) + ( -10 ) + ( -5 )

= - 25 .

a)217+[43+(-217)+(-23)]

=217+43-217-23

=(217-217)+(43-23)

=0+20

=20

b)273+(-123)

=273-123

=150

c)1+(-3)+(-5)+(-7)+(-11)

=1-3-5-7-11

=-2-5-7-11

=-(2+5+7+11)

-25

THANK YOU TẤT CẢ MỌI NGƯỜI

\(\dfrac{7}{9}\)

\(\dfrac{43}{32}\)

\(\dfrac{1}{3}\)

\(\dfrac{45}{63}+\dfrac{28}{63}-\dfrac{24}{63}=\dfrac{49}{63}=\dfrac{7}{9}\)

\(\dfrac{31}{32}+\dfrac{11}{16}=\dfrac{31}{32}+\dfrac{22}{32}=\dfrac{43}{32}\)

\(\dfrac{5}{6}\times\dfrac{4}{3}-\dfrac{7}{9}=\dfrac{10}{9}-\dfrac{7}{9}=\dfrac{3}{9}=\dfrac{1}{3}\)

217 x 9 = 217 x (10-1)

= 217 x 10 - 217 x 1

= 2170 - 217 = 1953