\(A=1+\frac{1}{3}+1+\frac{1}{8}+1+\frac{1}{15}+...+1+\frac{1}{120}=\left(1+1+...+1\right)+\left(\frac{1}{1\times3}+\frac{1}{2\times4}+\frac{1}{3\times5}+...+\frac{1}{10\times12}\right)\)\(A=10+\frac{1}{2}\times\left(\frac{2}{1\times3}+\frac{2}{2\times4}+\frac{2}{3\times5}+...+\frac{2}{10\times12}\right)=10+\frac{1}{2}\times\left(1-\frac{1}{3}+\frac{1}{2}-\frac{1}{4}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{10}-\frac{1}{12}\right)\)\(A=10+\frac{1}{2}\times\left(1+\frac{1}{2}+\left(-\frac{1}{3}+\frac{1}{3}\right)+\left(-\frac{1}{4}+\frac{1}{4}\right)+\left(-\frac{1}{5}+\frac{1}{5}\right)+...+\left(-\frac{1}{10}+\frac{1}{10}\right)-\frac{1}{11}-\frac{1}{12}\right)\)\(A=10+\frac{1}{2}\times\left(1+\frac{1}{2}-\frac{1}{11}-\frac{1}{12}\right)=10+\frac{175}{264}=\frac{2815}{264}\)

\(8^7-2^{18}=\left(2^3\right)^7-2^{18}=2^{21}-2^{18}=2^{17}\left(2^4-2\right)=2^{17}.14\)

=>đpcm

1 her kichen have a refrigerator and an electric stove

=> has

2 students buy snacks and drinks at a break or after lunchtime

=> break

3 mai will has a birthday party next Friday

=> have

4 tuan loves to working in the garden

=>working

5 can i find some science books at English?

=> in

1. I ( finish ) have not finished doing my home work yet

2. I ( know ) have known Tam for some years

3. We ( attend ) have attended Tran Quoc Tuan high school for three years.

4 . Have you ever ( be ) been there ? 

5 . My father ( work ) have worked  for his company for 25 years

số ngày một người ăn là:

6 x 70 = 420 (ngày)

số ngày 20 người ăn là:

420 : 20 = 21 (ngày)

đáp số: 21 ngày.

sao có 8 chỗ trống mà 10 câu

Nhận thấy 3^151 > 3^150

Mà 3^150 = (3^2)^75 = 9^75

và 2^225 = (2^3)^75 = 8^75

=> 3^150 > 2^225             (Vì  9^75 > 8^75)

Mà 3^151 > 3^150 >2^225

Vậy 3^151 > 2^225

^^

Ta có

 A \(\in\)Z <=> n+10 chia hết cho 2n+8

           <=> 2n+20 chia hết cho 2n+8

           <=> 2n+20-(2n+8) chia hết cho 2n+8

            <=> 12 chia hết cho 2n+8

            <=> 2n+8 \(\in\) Ư₍₁₂₎

Mà n là số tự nhiên nên \(2n+8\ge8\)

Ta có \(Ư_{\left(12\right)}=\left(1;2;3;4;12;-1;-2;-3;-4;-6;-12\right)\)

=> 2n+8=12

=> 2n=4

=>n=2

Vậy số cần tìm là 2