D

d

a) Ta có: \(\dfrac{15}{7}>1\) (tử lớn hơn mẫu)

\(\dfrac{9}{14}< 1\) (tử nhỏ hơn mẫu)

Vậy: \(\dfrac{15}{7}>\dfrac{9}{14}\)

b) Ta có: 

\(\dfrac{899}{900}=1-\dfrac{1}{900}\)

\(\dfrac{1235}{1236}=1-\dfrac{1}{1236}\)

Mà: \(\dfrac{1}{900}>\dfrac{1}{1236}\)

Vậy: \(\dfrac{1235}{1236}>\dfrac{899}{900}\)

c) Ta có:

\(\dfrac{77}{75}=1+\dfrac{2}{75}\)

\(\dfrac{37}{35}=1+\dfrac{2}{35}\)

Mà: \(\dfrac{2}{75}< \dfrac{2}{35}\)

Vậy: \(\dfrac{37}{35}>\dfrac{77}{75}\)

\(\left\{{}\begin{matrix}\dfrac{15}{7}=\dfrac{30}{14}\\\dfrac{9}{14}< \dfrac{30}{14}\end{matrix}\right.\Rightarrow\dfrac{15}{7}>\dfrac{9}{14}\)

\(\left\{{}\begin{matrix}\dfrac{899}{900}=\dfrac{899.1236}{900.1236}=\dfrac{\text{1111164}}{900.1236}\\\dfrac{1235}{1236}=\dfrac{1235.900}{900.1236}=\dfrac{\text{1111500}}{900.1236}>\dfrac{\text{1111164}}{900.1236}\end{matrix}\right.\Rightarrow\dfrac{1235}{1236}>\dfrac{899}{900}\)

\(\left\{{}\begin{matrix}\dfrac{77}{75}=\dfrac{539}{525}\\\dfrac{37}{35}=\dfrac{555}{525}>\dfrac{539}{525}\end{matrix}\right.\Rightarrow\dfrac{77}{73}< \dfrac{37}{35}\)

\(\frac{19}{20}\)và \(\frac{4}{3}\)

Ta có:

\(\frac{19}{20}\)< 1 ; \(\frac{4}{3}\)> 1

Vậy phân số \(\frac{4}{3}\)lớn hơn phân số \(\frac{19}{20}\)

\(\frac{19}{20}\)và \(\frac{15}{29}\)

\(\Rightarrow\frac{19}{20}>\frac{19}{29}>\frac{15}{29}\)

Vậy : \(\frac{19}{20}>\frac{15}{29}\)

hoi ngu vkl

4/5<1va 6/7     vay 2 phan so bang nhau

Ta có : 2.10 = 5.4 (cùng = 20) ;  1.9 = 3.3 (cùng = 9)

Câu 5: B

Câu 5: B

Ta thấy : 13x 15 phân số thứ nhất  nếu quy đồng tử nó sẽ có tích như thế con phân số thứ 2

7x 27 thì từ đó => 13/27> 7/15 ròi

A=\(\frac{3}{4}.\frac{8}{9}.\frac{15}{16}.........\frac{899}{900}\)

A=\(\frac{1.3}{2.2}.\frac{2.4}{3.3}.\frac{3.5}{4.4}..........\frac{29.31}{30.30}\)

A=\(\frac{1.2.3.......29}{2.3.4.......30}.\frac{3.4.5........31}{2.3.4.......30}\)

A=\(\frac{1}{30}.\frac{2}{31}=\frac{1}{465}\)