1. a) -0,35 = -7/20 ; b) 1,14 = 57/50

  c) 2,108 = 527/250 ; -0,725 = -29/40

2. a) 0,2(3) = 0,2 + 0,0(3) = 0,2 + 0,3. 0,(1) = 0,2 + 0,3.1/9 = 1/5 + 1/30 = 7/30 

  b 1,4(51) = 1,4 + 0,0(51) = 7/5 + 5,1. 0,(01) = 7/5 + 5,1. 1/99 = 7/5 + 17/330 = 479/330

  c) -2,(412) = -2 - 0,(412) = -2 - 412. 0,(001) = -2 - 412. 1/999 = -2 - 412/999 = -2410/999

d) 3,1(45) = 3,1 + 0,0(45) = 3,1 + 4,5. 0,(01) = 3,1 + 4,5 . 1/99 = 3,1 + 1/22 = 173/55

3. Ta có: -2,(6).x = 0,1(6)

=> [-2 - 0,(1).6].x = (0,1 + 0,6. 0,(1)]

=> (-2 - 2/3)x = 0,1 + 1/15

=> -8/3x = 1/6

=>  x = 1/6 : (-8/3)

=> x = -1/16

Ta có: 0,35 = 35 100 = 7 20  

Nên tổng cả tử và mẫu là 7 + 20 = 27.

Chọn đáp án B.

\(-0.025=\dfrac{-25}{1000}=\dfrac{-1}{40}\)

\(-0.033=\dfrac{-33}{1000}\)

-0,025= \(\dfrac{-1}{40}\)

-0,033= \(\dfrac{-33}{1000}\)

-0,025 = \(\dfrac{-25}{1000}\)=\(\dfrac{-1}{40}\)

-0,033 = \(\dfrac{-33}{1000}\)

\(0,75=\dfrac{75}{100}=\dfrac{75:25}{100:25}=\dfrac{3}{4}\\ 0,8=\dfrac{8}{10}=\dfrac{8:2}{10:2}=\dfrac{4}{5}\\ 2,15=\dfrac{215}{100}=\dfrac{215:5}{100:5}=\dfrac{43}{20}\)

A) \(0,75=\dfrac{75}{100}=\dfrac{75:25}{100:25}=\dfrac{3}{4}\)

B) \(0,8=\dfrac{8}{10}=\dfrac{8:2}{10:2}=\dfrac{4}{5}\)

C) \(2,15=\dfrac{215}{100}=\dfrac{215:5}{100:5}=\dfrac{43}{20}\)

a) \(0,75=\dfrac{3}{4}\)

b) \(0,8=\dfrac{4}{5}\)

c) \(2,15=\dfrac{43}{20}\)

-0,225=-9/40

-0,033=-33/1000

a ) 1,75 = 7 4 b ) − 3,12 = − 78 25

c ) 0,63 = 63 100 . d ) − 2,19 = − 219 100