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

a= 9

b=45

A=9

B=45

a/\(30,395:217=0,14\)(dư 0,015)
b/\(\dfrac{5}{7}:\dfrac{9}{14}-\dfrac{17}{18}\)
\(=\dfrac{5}{7}\times\dfrac{14}{9}-\dfrac{17}{18}\)
\(=\dfrac{10}{9}-\dfrac{17}{18}\)
\(=\dfrac{20}{18}-\dfrac{17}{18}\)
\(=\dfrac{3}{18}=\dfrac{1}{6}\)

30395 : 217 = 140

dư 15

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

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

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

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

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

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

217(10-1)=2170-217=1953

217x9=1953 **** bạn nha

217 x 11

= 217 x (10 +1)

= 217 x 10 + 217 x 1

= 2170 + 217 = 2387

a) 217 - 320 : 4 = 217 - 80 = 137

b) 5025 : 5 - 25 : 5 = 1005 - 5 = 1000

c) 640 : 32 + 32 = 20 + 32 = 52

d) 2180 - 180 : 2 : 9 = 2180 - 10 = 2170