A)\(\dfrac{7}{20}-\left(\dfrac{5}{8}-\dfrac{2}{5}\right)\)

\(=\dfrac{7}{20}-\left(\dfrac{25}{40}-\dfrac{16}{40}\right)\)

\(=\dfrac{7}{20}-\dfrac{9}{40}\)

\(=\dfrac{14}{40}-\dfrac{9}{40}=\dfrac{5}{40}=\dfrac{1}{8}\)

B) \(\dfrac{5}{6}+\left(\dfrac{5}{9}-\dfrac{1}{4}\right)\)

\(=\dfrac{5}{6}+\left(\dfrac{20}{36}-\dfrac{9}{36}\right)\)

\(=\dfrac{5}{6}+\dfrac{11}{36}\).

\(=\dfrac{30}{36}+\dfrac{11}{36}=\dfrac{41}{36}\)

C) \(\dfrac{9}{10}-\left(\dfrac{2}{5}-\dfrac{3}{10}\right)+\dfrac{7}{20}\)

\(=\dfrac{9}{10}-\left(\dfrac{4}{10}-\dfrac{3}{10}\right)+\dfrac{7}{20}\)

\(=\dfrac{9}{10}-\dfrac{1}{10}+\dfrac{7}{20}\)

\(=\dfrac{18}{20}-\dfrac{2}{20}+\dfrac{7}{20}=\dfrac{23}{20}\)

a: =7/20-5/8+2/5

=14/40-25/40+16/40

=5/40=1/8

b: =5/6+5/9-1/4

=30/36+20/36-9/36

=41/36

c: =9/10-2/5+3/10+7/20

=12/10-2/5+7/20

=7/20+6/5-2/5

=7/20+4/5

=7/20+16/20

=23/20

81 : 9 + 10 = 9 + 10 = 19

20 x 9 : 2 = 180 : 2 = 90

81 : 9 + 10 = 9 + 10 = 19

20 x 9 : 2 = 180 : 2 = 90

81 : 9 + 10 = 9 + 10

= 19

20 x 9 : 2 = 180 : 2

= 90

\(\frac{1}{3}+\frac{2}{3}.-\frac{9}{20}\)

\(\frac{1}{3}+\frac{2.-9}{3.20}\)

\(\frac{1}{3}+-\frac{3}{10}\)

\(\frac{10}{30}+-\frac{3}{10}\)

\(\frac{1}{30}\)

ai trả lời nhanh và đúng mình tích

ai trả lời nhanh và đúng mình tích

20 x 9 : 2 = 180 : 2 = 90

20 x 9 : 2 = 180 : 2

= 90

1) A. 999.

2) C. 9.

1: A

2: C

Câu 1: A

Câu 2: C