1. Mary is taller than her brother.

2. A horse is bigger than a donkey.

3. Our hotel is cheaper than all the others in the town.

4. The Nile is the longest river in the world.

5. Everest is higher than Fansipan.

A nha

Ta có  \(\dfrac{1}{4}< \dfrac{a}{24}< \dfrac{1}{3}\)

\(\Rightarrow\dfrac{6}{24}< \dfrac{a}{24}< \dfrac{8}{24}\)

\(\Rightarrow6< a< 8\)

\(\Rightarrow a=7\)

Vậy a = 7.

1 giờ 2 phút = 1 giờ + \(\dfrac{1}{30}\) giờ = \(\dfrac{31}{30}\) giờ

x : 3 = 1148 - 597

x : 3 = 551

x = 551 x 3

x = 1653

1+2+3+...+79+80

= \(\dfrac{\left(80+1\right)x80}{2}\)= \(\dfrac{81x80}{2}\)=81x40=3240

Ta có \(\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}+...+\dfrac{1}{x\left(x+1\right)}=\dfrac{1}{3}-\dfrac{x+1}{324}\)

\(\Rightarrow\)\(\dfrac{4-3}{3.4}+\dfrac{5-4}{4.5}+\dfrac{6-5}{5.6}+...+\dfrac{\left(x+1\right)-x}{x\left(x+1\right)}=\dfrac{1}{3}-\dfrac{x+1}{324}\)

\(\Rightarrow\)\(\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+...+\dfrac{1}{x}-\dfrac{1}{x+1}=\dfrac{1}{3}-\dfrac{x+1}{324}\)

\(\Rightarrow\)\(\dfrac{1}{3}-\dfrac{1}{x+1}=\dfrac{1}{3}-\dfrac{x+1}{324}\)

\(\Rightarrow\)\(\dfrac{1}{3}-\dfrac{1}{3}=-\dfrac{x+1}{324}+\dfrac{1}{x+1}\)

\(\Rightarrow\)\(\dfrac{1}{x+1}-\dfrac{x+1}{324}=0\)

\(\Rightarrow\)\(\dfrac{1}{x+1}=\dfrac{x+1}{324}\)

\(\Rightarrow\)(x+1).(x+1)=324

\(\Rightarrow\)(x+1)²=324

\(\Rightarrow\)(x+1)² = 18² = (-18)²

TH1: (x+1)² = 18²

\(\Rightarrow\)x+1 = 18 

\(\Rightarrow\)x = 17

TH2: (x+1)² = (-18)²

\(\Rightarrow\)x+1 = -18 

\(\Rightarrow\)x = -19

Vậy x\(\in\)\(\left\{17;-19\right\}\)

Ta có  (2022.19 + 152.3) - (2022.19 - 7.7)

= 2022.19 + 152.3 - 2022.19 + 7.7

= (2022.19 - 2022.19) + 456 + 49

= 0 + 505 = 505

Ta có  (8x²yz).(4xy²)

= 8x²yz.4xy²

= (8.4).(x².x).(y.y²).z

= 32x³y³z

Vậy (8x²yz).(4xy²) = 32x³y³z.