`B=(2015+2016+2017)/(2016+2017+2018)`

`=2015/(2016+2017+2018)+2016/(2016+2017+2018)+2017/(2016+2017+2018)`

Vì `2015/(2016+2017+2018)<2015/2016`

`2016/(2016+2017+2018)<2016/2017`

`2017/(2016+2017+2018)<2017/2018`

`=>B<A`

Bài 5

B= \(\dfrac{2015}{2016+2017+2018}\)+\(\dfrac{2016}{2016+2017+2018}\)+\(\dfrac{2017}{2016+2017+2018}\)

Ta có:\(\dfrac{2015}{2016}\)>\(\dfrac{2015}{2016+2017+2018}\),\(\dfrac{2016}{2017}\)>\(\dfrac{2016}{2016+2017+2018}\),\(\dfrac{2017}{2018}\)>\(\dfrac{2017}{2016+2017+2018}\)

⇒A>B

Giải:

Ta có:

\(B=\dfrac{2015+2016+2017}{2016+2017+2018}\) 

\(B=\dfrac{2015}{2016+2017+2018}+\dfrac{2016}{2016+2017+2018}+\dfrac{2017}{2016+2017+2018}\) 

Vì \(\dfrac{2015}{2016}>\dfrac{2015}{2016+2017+2018}\) 

\(\dfrac{2016}{2017}>\dfrac{2016}{2016+2017+2018}\) 

\(\dfrac{2017}{2018}>\dfrac{2017}{2016+2017+2018}\) 

\(\Rightarrow A>B\) 

Chúc bạn học tốt!

Số tiền Nam mua sách: \(320000\times\dfrac{1}{4}=80000\) (đồng)

Số tiền Nam mua vở: \(90000:\dfrac{2}{3}=135000\) (đồng)

Số tiền Nam mua dụng cụ học tập: \(320000-\left(80000+135000\right)=105000\) (đồng)

a,\(\dfrac{2}{3}\)-\(\dfrac{5}{7}\).\(\dfrac{14}{25}\)

=\(\dfrac{2}{3}\)-\(\dfrac{2}{5}\)

=\(\dfrac{4}{15}\)

b,\(\dfrac{-2}{5}\).\(\dfrac{5}{8}\)+\(\dfrac{5}{8}\).\(\dfrac{3}{5}\)

=\(\dfrac{5}{8}\).(\(\dfrac{-2}{5}\)+\(\dfrac{3}{5}\))

=\(\dfrac{5}{8}\).\(\dfrac{1}{5}\)

=\(\dfrac{1}{8}\)

Giải:

a) \(\dfrac{2}{3}-\dfrac{5}{7}.\dfrac{14}{25}=\dfrac{2}{3}-\dfrac{2}{5}=\dfrac{4}{15}\) 

b) \(\dfrac{-2}{5}.\dfrac{5}{8}+\dfrac{5}{8}.\dfrac{3}{5}\) 

\(=\dfrac{5}{8}.\left(\dfrac{-2}{5}+\dfrac{3}{5}\right)\) 

\(=\dfrac{5}{8}.\dfrac{1}{5}\) 

\(=\dfrac{1}{8}\) 

c) \(\left(\dfrac{1}{2}\right)^2-1\dfrac{1}{2}+0,5.\dfrac{12}{5}+5\%\) 

\(=\dfrac{1}{4}-\dfrac{3}{2}+\dfrac{1}{2}.\dfrac{12}{5}+\dfrac{1}{20}\) 

\(=\dfrac{-5}{4}+\dfrac{6}{5}+\dfrac{1}{20}\) 

\(=0\) 

Chúc bạn học tốt!

c,\(\left(\dfrac{1}{2}\right)^2\)-1\(\dfrac{1}{2}\)+0,5.\(\dfrac{12}{5}\)+5%

=\(\dfrac{1}{4}\)-\(\dfrac{3}{2}\)+\(\dfrac{1}{2}\).\(\dfrac{12}{5}\)+\(\dfrac{1}{20}\)

=\(\dfrac{1}{4}\)-\(\dfrac{3}{2}\)+\(\dfrac{6}{5}\)+\(\dfrac{1}{20}\)

=\(\dfrac{-5}{4}\)+\(\dfrac{6}{5}\)+\(\dfrac{1}{20}\)

=\(\dfrac{-1}{20}\)+\(\dfrac{1}{20}\)

=0

=

Giúp mình đi các bạn 🥺

tài nguyên rừng nước ta :

Nằm trong vùng thuộc khu hệ rừng mưa nhiệt đới, rừng nước ta nổi tiếng về tài nguyên gỗ, nhất là đặc sản có giá trị. ta có 14,352 triệu ha rừng, chiếm tỷ lệ 43,8% so với diện tích tự nhiên. 9,3 triệu, trong đó có những rừng mới trồng.

-em tưới nước cho cây xanh tốt hơn 

-bón phân cho cây

14.He asked me to help my withe the exercises.

15.He said he left early on Friday.

16.She asked me where he would meet that night.

17.Milk could be used for making butter and cheese.

18.Bottles of milk are brought to houses by the milkman.

19.A lot of beautiful toys are made from recyced plastic.

20.The concerts usually are held at the university.

a) Ta có: \(A=\dfrac{7}{12}+\dfrac{5}{12}:6-\dfrac{11}{36}\)

\(=\dfrac{7}{12}+\dfrac{5}{72}-\dfrac{11}{36}\)

\(=\dfrac{42}{72}+\dfrac{5}{72}-\dfrac{22}{72}\)

\(=\dfrac{25}{36}\)

b) Ta có: \(B=\left(\dfrac{4}{5}+\dfrac{1}{2}\right):\left(\dfrac{3}{13}-\dfrac{8}{13}\right)\)

\(=\left(\dfrac{8}{10}+\dfrac{5}{10}\right):\dfrac{-5}{13}\)

\(=\dfrac{13}{10}\cdot\dfrac{13}{-5}\)

\(=-\dfrac{169}{50}\)

c) Ta có: \(C=\left(\dfrac{2}{3}-\dfrac{1}{4}+\dfrac{5}{11}\right):\left(\dfrac{5}{12}+1-\dfrac{7}{11}\right)\)

\(=\left(\dfrac{88}{132}-\dfrac{33}{132}+\dfrac{60}{132}\right):\left(\dfrac{55}{132}+\dfrac{132}{132}-\dfrac{84}{132}\right)\)

\(=\dfrac{115}{132}\cdot\dfrac{132}{103}=\dfrac{115}{103}\)

câu 12 :A

câu 13 :B

câu 14 :D

câu 15 :A

câu 16 :D

câu 17 :A

câu 18 :C

câu cuối mik chx chắc lắm 

a: Xét ΔAFD vuông tại F và ΔCEB vuông tại E có

AD=CB

góc FAD=góc ECB

=>ΔAFD=ΔCEB

=>DF=EB

Xét tứ giác DFBE có

DF//BE

DF=BE

=>DFBE là hình bình hành

b: S CAB=S CAD

=>CH*AB=CK*AD

=>CH*AB=CK*BC

=>CH/BC=CK/AB

Xét ΔCHK và ΔBCA có

CH/BC=CK/BA

góc HCK=góc CBA

Do đó: ΔCHK đồng dạng với ΔBCA