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a) 2 x 76 x 500 = (2 x 500) x 76
= 1 000 x 76
= 76 000
b) 5 x 300 x 800 = (5 x 800) x 300
= 4 000 x 300
= 1 200 000
c) 70 x 21 + 30 x 21 = 21 x (70 + 30)
= 21 x 100
= 2 100
d) 81 x 28 – 81 x 18 = 81 x (28 – 18)
= 81 x 10 = 810
9/5 + 4/7 + 6/5 + 3/7
= ( 9/5 + 6/5 ) + ( 4/7 + 3/7)
= 3 + 1
= 4
9/5 + 4/7 + 6/5 + 3/7 = (9/5 + 6/5) + (4/7 + 3/7)
= 15/5 + 7/7
= 3 + 1
= 4
1/2 x 45/33 x 1/9 x 11/6 = (1/2 x 1/9) x (45/33 x 11/6)
= 1/18 x 45/18
= 5/2
a) 216 x 5 x 2
= 216 x (5x2)
= 216 x 10 = 2160
b) 4 x 76 x 25
= (4 x 25) x 76
= 100 x 76 = 7600
c) 5 x 19 x 2
= ( 5 x2 ) x 19
= 10 x 19 = 190
d) 125 x 23 x 8
= ( 125 x 8) x 23
= 1000 x 23 = 23000
a.\(\dfrac{2}{3}\times\dfrac{4}{9}+\dfrac{2}{3}\times\dfrac{5}{9}=\dfrac{2}{3}\times\left(\dfrac{4}{9}+\dfrac{5}{9}\right)=\dfrac{2}{3}\times1=\dfrac{2}{3}\)
b.\(\dfrac{7}{5}\times\dfrac{3}{4}-\dfrac{1}{2}\times\dfrac{3}{4}=\dfrac{3}{4}\times\left(\dfrac{7}{5}-\dfrac{1}{2}\right)=\dfrac{3}{4}\times\dfrac{9}{10}=\dfrac{27}{40}\)
c.\(\left(\dfrac{5}{6}+\dfrac{5}{8}\right)\times\dfrac{2}{3}=\dfrac{35}{24}\times\dfrac{2}{3}=\dfrac{35}{36}\)
a) 2/3 x 4/9 + 2/3 x 5/9
=2/3 x ( 4/9 + 5/9)
= 2/3 x 1
= 2/3
b, 7/5 x 3/4 - 1/2 x 3/4
= ( 7/5 - 1/2 ) x 3/4
= 9/10 x 3/4
= 21/40
c, ( 5/6 + 5/8 ) x 2/3
= 35/24 x 2/3
= 35/36
a) 13 x 5 x 2
= 13 x (5 x 2)
= 13 x 10 = 130
5 x 2 x 34
= (5 x 2 ) x 34
= 10 x 34 = 340
b) 2 x 26 x 5
= 26 x (2 x 5)
= 26 x 10 = 260
5 x 9 x 3 x 2
= (9 x 3) x (5 x 2)
= 27 x 10 = 270
Hướng dẫn giải:
a) 4 x 78 x 5 = (4 x 5) x 78 = 20 x 78 = 1560
b) 2 x 99 x 5 = (2 x 5) x 99 = 10 x 99 = 990
c) 6 x 31 x 5 = (6 x 5) x 31 = 30 x 31 = 930
d) 8 x 63 x 5 = (8 x 5) x 63 = 40 x 63 = 2520
