1: 

a: \(1\dfrac{2}{3}-\dfrac{7}{12}x=\dfrac{-5}{24}\cdot\dfrac{8}{-15}\)

=>\(\dfrac{5}{3}-\dfrac{7}{12}x=\dfrac{5}{15}\cdot\dfrac{8}{24}=\dfrac{1}{9}\)

=>\(\dfrac{7}{12}x=\dfrac{5}{3}-\dfrac{1}{9}=\dfrac{14}{9}\)

=>\(x=\dfrac{14}{9}:\dfrac{7}{12}=\dfrac{14}{9}\cdot\dfrac{12}{7}=2\cdot\dfrac{4}{3}=\dfrac{8}{3}\)

b: \(\dfrac{25}{-30}=\dfrac{15}{x}\)

=>\(\dfrac{15}{x}=\dfrac{5}{-6}\)

=>\(x=\dfrac{15\cdot\left(-6\right)}{5}=-3\cdot6=-18\)

2:

\(\left(\dfrac{1}{32}\right)^7=\left[\left(\dfrac{1}{2}\right)^5\right]^7=\left(\dfrac{1}{2}\right)^{35}\)

\(\left(\dfrac{1}{16}\right)^9=\left[\left(\dfrac{1}{2}\right)^4\right]^9=\left(\dfrac{1}{2}\right)^{36}\)

mà 35<36 và 1/2<1

nên \(\left(\dfrac{1}{2}\right)^{35}>\left(\dfrac{1}{2}\right)^{36}\)

=>\(\left(\dfrac{1}{32}\right)^7>\left(\dfrac{1}{16}\right)^9\)

\(\dfrac{25}{-30}=\dfrac{15}{x}\)

=>\(\dfrac{15}{x}=\dfrac{-5}{6}\)

=>\(x=15\cdot\dfrac{6}{-5}=-3\cdot6=-18\)

25/-30 = 15/x
=> 25 . x = -30 . 15
=> 25 . x = -450
=> x = -450 / 25
=> x = -18
Vậy x = -18

uki

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7 are usuallly

8 always arrives

a: Tỉ lệ phần trăm chất béo có trong 100gam gạo là:

1,3:100=1,3%

b:

1,5kg=1500(gam)

Trong 1,5kg thì khối lượng chất béo là:

1500:100*1,3=19,5(gam)

a) Tỉ lệ phần trăm khối lượng chất béo có trong 100 g gạo là:
(1,3 :100) x 100% = 1,3% 
b) Đổi: 1,5 kg = 1500 (g)
Khối lượng chất béo có trong 1,5 kg gạo là:
1500 x 1,3% = 19,5 (g)
Đáp số: a) 1,3%.
              b) 19,5 gam chất béo.

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ĐKXĐ: n<>-1/5

Để \(\dfrac{4n-12}{5n+1}\) nguyên thì \(4n-12⋮5n+1\)

=>\(20n-60⋮5n+1\)

=>\(20n+4-64⋮5n+1\)

=>\(-64⋮5n+1\)

=>\(5n+1\in\left\{1;-1;2;-2;4;-4;8;-8;16;-16;32;-32;64;-64\right\}\)

=>\(n\in\left\{0;-\dfrac{2}{5};\dfrac{1}{5};-\dfrac{3}{5};\dfrac{3}{5};-1;\dfrac{7}{5};-\dfrac{9}{5};3;-\dfrac{17}{5};\dfrac{31}{5};-\dfrac{33}{5};\dfrac{63}{5};-13\right\}\)

mà n nguyên

nên \(n\in\left\{0;-1;3;-13\right\}\)

Lời giải:

Gọi số cần tìm là $a$ (điều kiện $a>20$). Theo bài ra:

$185-20\vdots a$

$\Rightarrow 165\vdots a$

$250-19\vdots a$

$\Rightarrow 231\vdots a$

$\Rightarrow a=ƯC(165,231)$

$\Rightarrow ƯCLN(165,231)\vdots a$

$\Rightarrow 33\vdots a$

Mà $a>20$ nên $\Rightarrow a=33$

1: ĐKXĐ: \(n\ne-\dfrac{1}{2}\)

Để \(\dfrac{3n+2}{2n+1}\) nguyên thì \(3n+2⋮2n+1\)

=>\(6n+4⋮2n+1\)

=>\(6n+3+1⋮2n+1\)

=>\(1⋮2n+1\)

=>\(2n+1\in\left\{1;-1\right\}\)

=>\(n\in\left\{0;-1\right\}\)(nhận)

2:

ĐKXĐ: n<>-1/5

Để \(\dfrac{8n+12}{5n+1}\) là số nguyên thì

\(8n+12⋮5n+1\)

=>\(40n+60⋮5n+1\)

=>\(40n+8+52⋮5n+1\)

=>\(52⋮5n+1\)

=>\(5n+1\in\left\{1;-1;2;-2;4;-4;13;-13;26;-26;52;-52\right\}\)

=>\(n\in\left\{0;-\dfrac{2}{5};\dfrac{1}{5};-\dfrac{3}{5};\dfrac{3}{5};-1;\dfrac{12}{5};-\dfrac{14}{5};5;-\dfrac{27}{5};\dfrac{51}{5};-\dfrac{53}{5}\right\}\)

mà n nguyên

nên \(n\in\left\{0;-1;5\right\}\)