`a, 1000 : 100 = 10`

`b, 75 xx 100 = 7500`

`c, 900 xx 10 = 9000`

`d, 8 xx 100 : 10 : 10 xx 10000 = 80000`

\(a,1000:100=10\\ b,75\times100=7500\\ c,900\times10=9000\\ d,8\times100:10:10\times10000\\ =800:10:10\times10000=8\times10000=80000\)

\(\dfrac{x}{7}=\dfrac{22}{7}\\ =>x=22\)

\(\dfrac{x}{7}=\dfrac{22}{7}\)
\(x=22\)
 

Chiều rộng khu đất:
\(72:\left(1+2\right)\times1=24\left(km\right)\)
Chiều dài khu đất:
\(24\times2=48\left(km\right)\)
Chu vi khu đất:
\(\left(48+24\right)\times2=144\left(km\right)\)

Gọi chiều rộng là `x`

Chiều dài là `2x`

Ta có: `x . 2x = 72`

`<=> 2x^2 = 72`

`<=> x = 6`

`=> 2x= 12`

Chu vi = `(12+6) xx 2 = 36 km`

`x xx 3=14`

`=>x=14:3`

`=>=14/3`

`x = 14/3`

2x73y chia 2 dư 1 khi y\(\in\left\{3;5;7;9\right\}\)

2x73y chia 5 dư 4 khi y\(\in\left\{4;9\right\}\)

=>y=9

=>2x739 chia 9 dư 5 khi \(2+x+7+3+9=\left(21+x\right)⋮9\)

=>x=6

Vậy số cần tìm là 26739 với x=6 y=9

`a, 350, 222, 456, 800`

`b, 125, 350, 555, 800`

`c, 350, 800`

`d, 222, 456`

`e, 125, 555`

`f, 222, 555, 456`

`g, 350, 125, 800

`g, 350, 125, 800`

`h, 222, 456`

\(\dfrac{8}{24}=\dfrac{2}{6}=\dfrac{1}{x}\\ =>\dfrac{1}{3}=\dfrac{1}{3}=\dfrac{1}{x}\\ =>x=3\)

\(\dfrac{8}{24}=\dfrac{2}{6}=\dfrac{1}{3}\)

\(75\times\left(x+157\right)=24450\\ =>x+157=24450:75\\ =>x+157=326\\ =>x=326-157\\ =>x=169\)

`75 xx (x+157)=24450`

`=> x+157=24450:75`

`=>x+157=326`

`=>x=326-157`

`=>x=169`

`15/13 -(4/7 + 2/13)`

`= 15/13 -4/7-2/13`

`=(15/13-2/13)-4/7`

`= 13/13-4/7`

`=1-4/7`

`=7/7-4/7`

`=3/7`

\(\dfrac{15}{13}-\left(\dfrac{4}{7}-\dfrac{2}{13}\right)\)
\(=\dfrac{15}{13}-\dfrac{4}{7}-\dfrac{2}{13}\)

\(=\left(\dfrac{15}{13}-\dfrac{2}{13}\right)-\dfrac{4}{7}\)

\(=1-\dfrac{4}{7}\)

\(=\dfrac{3}{7}\)

\(\dfrac{60}{36}=\dfrac{60:12}{36:12}=\dfrac{5}{3}\)