Đáp án: A

Chọn A

1/5m =0,2m

Chiều dài hình chữ nhật là: (2:2+0,2):2=0,6m

Diện tích hình chữ nhật là : 0,6 .( 0,6-0,2) = 0,24m²

nửa chu vi hcn: 2:2=1(m)=100 cm

1/5 m= 20cm

chiều dài: (100+20):2= 60(cm)

chiều rộng: (100-20):2= 40(cm)

diện tích: 60x40=2400(cm²)

Ta biết rằng hai cạnh có độ dài bằng nhau và bằng x, ta có  phương trình:

2(0,4 + 0,6 + x) = 3,2

\(\Leftrightarrow\) 0,4 + 0,6 + x = 1,6

\(\Leftrightarrow\) 1 + x = 1,6

\(\Leftrightarrow\) x = 0,6

Vậy, giá trị của x là 0,6m.

Do đó, phần còn lại của khung hình quanh bức tranh có chiều rộng bằng nhau và bằng 0,6m.

Chiều dài là:

\(\dfrac{27}{2}:\dfrac{10}{3}=\dfrac{27}{2}\cdot\dfrac{3}{10}=\dfrac{81}{20}\left(dm\right)\)

Chiều dài hình chữ nhật là:

\(\dfrac{27}{2}:\dfrac{10}{3}=\dfrac{81}{20}\left(dm\right)\)

Đáp số: \(\dfrac{81}{20}dm\)

A

A

A nha 

Bằng 11,31

Nữa chu vi bức tranh :

 16,8 : 2 = 8,4 ( m )

Chiều dài bức tranh :

 ( 8,4 + 3,2 ) : 2 = 5,8 ( m )

Chiều rộng bức tranh :

5,8 - 3,2 = 2,6 ( m )

Diện tích bức tranh :

5,8 x 2,6 = 15,08 ( m² )

Dùng hết số giấy màu :

15,08 : 1 x 0,75 = 11,31 ( kg )

đ/s : 11,31 kg 

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tìm n để phân số 3n+2/ 7n+1 tối giản

                   Đổi : 1m2dm = 120 cm

Chu vi bức tranh đó là :

              ( 120 + 80 ) x 2 = 400 ( cm )

Vậy chiều dài khung nhôm cần để thành bức tranh hình chữ nhật đó là 400cm

Đổi: 1 m 2 dm= 120 cm

cHU VI:

(120+80)x2=400(cm)

Đáp số: 400 cm

Đổi : 1m2dm = 120 cm

Chu vi bức tranh đó là :             

( 120 + 80 ) x 2 = 400 ( cm )

Đ/S: 400 cm