a, Chiều rộng mảnh đất là:
      60 * 2/3=40(m)
    Diện tích mảnh đất là:
      60 * 40=2400(m²)
b, Trên mảnh đất thu được số tấn ngô là:
      2400 * 5/4=3000(kg)
                       =3 tấn

1.Who is the girl?
2.Where is your address?
3.That time is this?
4. (mih ko biết)

1.Who is the girl?
2.Where is your address?
3.That time is this?

Cửa hàng đã bán số gạo là:

\(4\times\dfrac{4}{5}=\dfrac{16}{5}\) (tấn)

Số gạo còn lại là:

\(4-\dfrac{16}{5}=\dfrac{4}{5}\) (tấn)

Đã bán số gạo là:
 4 * 4/5=16/5
Còn lại số gạo là:
4-16/5=4/5

$\frac35\times5+12\times35+3:\frac53$

$=\frac35\times5+12\times35+3\times\frac35$

$=\frac35\times(5+12+3)$

$=\frac35\times(17+3)$

$=\frac35\times20=12$

\(\dfrac{3}{5}\) x 5 + 12 x \(\dfrac{3}{5}\) + 3 : \(\dfrac{5}{3}\)

= \(\dfrac{3}{5}\) x 5 + 12 x \(\dfrac{3}{5}\) + 3 x \(\dfrac{3}{5}\)

= \(\dfrac{3}{5}\) x (5 + 12 + 3)

= \(\dfrac{3}{5}\) x (17 + 3)

= \(\dfrac{3}{5}\) x 20

= 12

Ta có: \(\dfrac{2020}{2121}=\dfrac{2020:101}{2121:101}=\dfrac{20}{21}\)

Lại có: \(\dfrac{202020}{212121}=\dfrac{202020:10101}{212121:10101}=\dfrac{20}{21}\)

Vì \(\dfrac{20}{21}=\dfrac{20}{21}\) nên  \(\dfrac{2020}{2121}=\dfrac{202020}{212121}\)

2/7 , 3/5 , 2/5 , 3/4 , 4/4 , 3/5 , 3/2

Rồi bạn nhé.

\(\left(1-\dfrac{1}{5}\right)\times\left(1-\dfrac{1}{6}\right)\times\left(1-\dfrac{1}{7}\right)\times\left(1-\dfrac{1}{8}\right)\)

\(=\dfrac{4}{5}\times\dfrac{5}{6}\times\dfrac{6}{7}\times\dfrac{7}{8}\)

\(=\dfrac{4\times5\times6\times7}{5\times6\times7\times8}=\dfrac{4}{8}=\dfrac{1}{2}\)

\(\left(\dfrac{1}{20}+\dfrac{1}{80}\right)\times160000\)

\(=\dfrac{1}{20}\times160000+\dfrac{1}{80}\times160000\)

\(=8000+2000=10000\)

Sửa đề: \(\dfrac{1}{1\times3}+\dfrac{2}{3\times7}+\dfrac{3}{7\times13}+\dfrac{4}{13\times21}+\dfrac{5}{21\times31}\)

\(=\dfrac{1}{2}\times\left(\dfrac{2}{1\times3}+\dfrac{4}{3\times7}+\dfrac{6}{7\times13}+\dfrac{8}{13\times21}+\dfrac{10}{21\times31}\right)\)

\(=\dfrac{1}{2}\times\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{21}+\dfrac{1}{21}-\dfrac{1}{31}\right)\)

\(=\dfrac{1}{2}\times\left(1-\dfrac{1}{31}\right)=\dfrac{1}{2}\times\dfrac{30}{31}=\dfrac{15}{31}\)