Số giây cần đết cắt hết 100 khúc vải là:

\(100\times3=300\) (giây)

Đáp số: 300 giây 

300 giây ko có đúng

Số số hạng của A:

103 - 1 + 1 = 103 (số)

A = (-1 + 2) + (-3 + 4) + (-5 + 6) + ... + (-101 + 102) - 103

= 1 + 1 + 1 + ... + 1 - 103 (56 số 1)

= 56 - 103

= -47

d.

\(\dfrac{2^3.5^4.49}{35.2^2.175}=\dfrac{2^3.5^4.7^2}{5.7.2^2.7.5^2}=\dfrac{2^3.5^4.7^2}{2^2.5^3.7^2}=2.5=10\)

\(\dfrac{12.2^a}{3^2.8^b}=\dfrac{3.2^2.2^a}{3^2.\left(2^3\right)^b}=\dfrac{3.2^{a+2}}{3^2.2^{3b}}=\dfrac{2^{a-3b+2}}{3}\)

\(\dfrac{2.4+2.4.8+4.8.16+8.16.32}{3.4+2.6.8+4.12.16+8.24.32}\)

\(=\dfrac{1.2.4+2.1.2.2.2.4+4.1.4.2.4.4+8.1.8.2.8.4}{3.4+2.1.2.3.2.4+4.1.4.3.4.4+8.1.8.3.8.4}\)

\(=\dfrac{1.2.4+2^3.1.2.4+4^3.1.2.4+8^3.1.2.4}{1.3.4+2^3.1.3.4+4^3.1.3.4+8^3.1.3.4}\)

\(=\dfrac{1.2.4.\left(1+2^3+4^3+8^3\right)}{1.3.4.\left(1+2^3+4^3+8^3\right)}\)

\(=\dfrac{2}{3}\)

Do \(\left(a,b\right)=16\), đặt \(\left\{{}\begin{matrix}a=16x\\b=16y\end{matrix}\right.\) với \(\left(x,y\right)=1\)

\(a+b=128\Rightarrow16x+16y=128\)

\(\Rightarrow x+y=8\)

Mà \(\left(x,y\right)=1\Rightarrow\left(x;y\right)=\left(1;7\right);\left(7;1\right);\left(3;5\right);\left(5;3\right)\)

\(\Rightarrow\left(a;b\right)=\left(16;112\right);\left(112;16\right);\left(48;80\right);\left(80;48\right)\) có 4 cặp thỏa mãn

1. C
2, B
3, D
4, C
5,A 
6, B

1 C

2 B

3 D

4 C

5 A

6 B

1 Ha noi is a large city and is also interesting

2 The people are very friendly and the weather is sunny

3 Ha Long Bay is one of the most popular tourist attractions in Vietnam

4 Nha Trang is famous for its beautiful beaches and seafood

5 I bought some pottery to make a gift for my family and friends

1 It is in the Northern part of South Korea

2 10 million people live in Seoul

3 Yes, it is

4 It takes 40 minutes to travel from Seoul to Incheon Airport by train

5 Yes, they are

6 The War Memorial of Korea and Namsan Seoul Tower are popular tourist destinations in Seoul