1. a) 4, 360 = 4, 36
15, 500 = 15, 5
258, 0070 = 258, 007
90, 6000 = 90, 6
0, 08000 = 0, 08
630, 300 = 630, 3
b)
5,4 = 5, 400
13,02 = 13, 020
20,49 = 20, 490
9, 63 = 9, 630
11, 1300 = 11, 130
0, 00900 = 0, 009
2. a)
Ba số thập phân bằng 19, 80: 19,8 ; 19, 800 ; 19, 8000
b) 
3,4 = $\frac{34}{10}$    Đ
3,4 = $\frac{3400}{1000}$ Đ

3,4 = $\frac{340}{100}$ Đ
3,4 = $\frac{34}{100}$  S
3. a)
0,5 = $\frac{5}{10}$​ 
​b) 3,2 = $\frac{32}{10}$
c, 15,04 = $\frac{1504}{10000}$
d, 0, 07 = $\frac{7}{100}$
e, 5,15 = $\frac{515}{100}$
g, 2,409 = $\frac{2409}{1000}$
k, 0,009 = $\frac{9}{1000}$
i, 9,463 = $\frac{9463}{1000}$
l, 30,25 = $\frac{3025}{1000}$

4. Các số là : 1,23 ; 1,32 ; 2,31 ; 2,13 ; 3,21 ; 3, 12

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