A) x = 5

B) x = 18

C) thì ko bít

a. \(\dfrac{x}{5}=\dfrac{25}{75}\)

\(x:5=25:75=\dfrac{1}{3}\)

\(x=\dfrac{1}{3}\text{×}5=\dfrac{5}{3}\)

b. \(\dfrac{16}{x}=\dfrac{8}{9}\)

\(16:x=8:9\)

\(x=16:8:9=\dfrac{2}{9}\)

c. \(\dfrac{20}{35}=\dfrac{x}{14}\)

\(x:14=20:35=\dfrac{4}{7}\)

\(x=\dfrac{4}{7}\text{×}14=8\)

Lời giải:
a.

$x=\frac{25}{75}\times 5=\frac{25\times 5}{75}=\frac{25\times 5}{25\times 3}=\frac{5}{3}$

b.

$x=16: \frac{8}{9}=16\times \frac{9}{8}=\frac{8\times 2\times 9}{8}=18$

c.

$x=\frac{20}{35}\times 14=\frac{20\times 14}{35}=\frac{4\times 5\times 7\times 2}{5\times 7}=4\times 2=8$

a)8/25 ;  9/25 ; 12/25; 24/25

b)7/3 ; 7/9 ;7/8 ; 7/26

c)3/5 ; 9/10; 14/15; 23/30

d)5/9; 11/15 ; 11/18 ;14/15

I

1.What type of energy do you use at home?
2.John uses low energy light bulbs to save electricity.
3.Mai can't go to the cinema at present because she is studying for her exam.
4.What book are you currently reading?
5.She is not swimming in the swimming pool at the moment.
6.Scientists are looking for a new energy source to replace coal now

II.

1. Coal is more expensive and more polluting than natural gas.

2. We are looking for cheap and clean and effective sourced of energy..

3.. You should switch off electrical appliances when they aren’t in use.

4. Despite being the most polluting of fossil fuels, coal is still the largest sources of energy worldwide.

5. People will use biogas for fuel in homes and for transport

24/12

24/12

1965cm²

1965 cm²

1965cm²

help me

Nửa chu vi hcn là : 5/2 : 2 = 5/4

Chiều dài hcn là : ( 5/4 + 1/4 ) : 2 = 3/4

Chiều rộng hcn là : 5/4 - 3/4 = 1/2

Nửa chu vi là:

5/2:2=5/4(m)

Chiều dài là:

(5/4+1/4):2=3/4(m)

Chiều rộng là:

5/4-3/4=1/2(m)

ĐS:...

Nửa chu vi hcn là:
\(\dfrac{5}{2}:2=\dfrac{5}{4}\left(m\right)\)

Chiều dài hcn là:
\(\left(\dfrac{5}{4}+\dfrac{1}{4}\right):2=\dfrac{3}{4}\left(m\right)\)

Chiều rộng hcn là:

\(\dfrac{5}{4}-\dfrac{3}{4}=\dfrac{1}{2}\left(m\right)\)