a)

 \(3:8=\dfrac{3}{8}\)

\(8:9=\dfrac{8}{9}\)

\(4:7=\dfrac{4}{7}\)

\(12:5=\dfrac{12}{5}\)

b)

 \(7=\dfrac{7}{1}\)

\(9=\dfrac{9}{1}\)

\(21=\dfrac{21}{1}\)

\(40=\dfrac{40}{1}\)

− 5 6 = − 10 24 ; 3 − 8 = − 9 24 ; 7 12 = 14 24 ; − 25 100 = − 1 4 = − 6 24 72 108 = 2 3 = 16 24 ; 10 60 = 1 6 = 4 24

− 5 6 = − 10 24 ; 3 − 8 = − 9 24 ; 7 12 = 14 24 ; − 25 100 = − 1 4 = − 6 24 72 108 = 2 3 = 16 24 ; 10 60 = 1 6 = 4 24

\(a,-\dfrac{10}{21}=\dfrac{-2}{7}.\dfrac{5}{3}=\dfrac{-2}{3}.\dfrac{5}{7}\\ b,\dfrac{2}{21}=\dfrac{1}{3}.\dfrac{2}{7}=\dfrac{1}{7}.\dfrac{2}{3}\\ c,\dfrac{8}{15}=\dfrac{2}{3}.\dfrac{4}{5}=\dfrac{4}{3}.\dfrac{2}{5}\)

1.
a) 10=\(\dfrac{40}{4}\)

b) 25= \(\dfrac{100}{4}\)

2.

a) 11=\(\dfrac{11}{1}\)

b) 276=\(\dfrac{276}{1}\)

c) 158=\(\dfrac{158}{1}\)

3.

\(\dfrac{1}{1};\dfrac{2}{2};\dfrac{3}{3};\dfrac{4}{4};\dfrac{5}{5}\)

\(\dfrac{-5}{6}=\dfrac{-5\times4}{6\times4}=\dfrac{-20}{24}\)

\(\dfrac{3}{-8}=\dfrac{3\times\left(-3\right)}{-8\times\left(-3\right)}=\dfrac{-9}{24}\)

\(2=\dfrac{48}{24}\)

\(\dfrac{-25}{100}=\dfrac{-1}{4}=\dfrac{-1\times6}{4\times6}=\dfrac{-6}{24}\)

\(\dfrac{72}{108}=\dfrac{2}{3}=\dfrac{2\times8}{3\times8}=\dfrac{16}{24}\)

Đáp án là D

A=1/12+1/8+1/24+1/16

A=5/16

A=5x3/16x3

A=15/48

=> A dưới dạng một phân số có mẫu số là 48 thì tử số của phân số đó là 15

 k cho minh