Xem đàn vịt hiện tại là 100% theo lời vịt trời ta có: 

1/2 = 50% ;   1/4 = 25%

100% + 100% + 50% + 25% = 275%

275% đàn vịt được 99 con vậy 100% đàn vịt là : 

99 x 100 : 275  = 36 con

nếu đúng thì chọn câu trả lời của mình nhe

12.43 + 6.14 + 15.53

= 12.43 + 6.2.7 + 15.53

= 12.43 + 12.7 + 15.53

= 12.(43 + 7) + 15.53

= 12.50 + 15.53

= 4.3.5.10 + 15.53

= 15.40 + 15.53

= 15.93

= 1395

tai sao a>29 de tat ca cac thua so deu la so tu nhien

diện tích hình vuông là

(20+20)*(20+20) = 1600

diện tích phần tô màu bằng diện tích hình tròn nên ta có 

20*20*3.14=1256

diện tích phần ko tô màu là 

1600-1256=344

a)5x+7y=112

tách ra các giá trị nguyên

tìm 1 nghiệm riêng

1*2 + 2*3 + 3*4 + 4*5 + ... + 9*10

= 1/3 . ( 1.2.3 + 2.3.3 + 3.4.3 + 4.5.3 + ... + 9.10.3)

= 1/3 . [ 1.2.3 + 2.3.(4-1) + 3.4.(5-2) + 4.5.(6-3) + ... + 9.10.(11-8)]

= 1/3 . ( 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + 4.5.6 - 3.4.5 + ... + 9.10.11 - 8.9.10)

= 1/3 . 9.10.11

= 3.10.11 = 330

Ta có:\(\frac{n+5}{n}=\frac{n}{n}+\frac{5}{n}=1+\frac{5}{n}\)

Để A là số nguyên thì \(\frac{5}{n}\) là số nguyên

\(\Rightarrow\)5 chia hết cho n

\(\Rightarrow\)n\(\in\)Ư(5)={-5,-1,1,5}

rewrite the sentences with the words given.
1.Iam a faster worker than Tom is.
Tom.................doesn't work as fast as i do......................
2.Lan's English is more fluent than my sister's.(fluently)
My sister speaks English more fluently than Lan does..........................
3.A snail is slower than a crab.(slowly)
A snail moves...............slowlier than a crab.....................
4.Phong is a faster swimmer than Phuc.(fast)
Phong swims...........faster than Phuc does................
5.It's a pity my brother doesn't pass the driving test.
I wish.............my brother passes the driving tesr....................
6.Nam is better at English than Linh.
Linh..............isn't as better at English as Nam is..................
7.These pupils were very lazy.They couldn't complete their test successfully.
These pupils.............weren't hard..........enough............to complete their test...................
8.Did Mary buy this beautiful dress?
....................Was this beautiful dress bought by Mary?..........................
9.I won't hang these old pictures in the living room.
.......................The old pictures won't be hung in the living room............................
10.The boys said:"We have to try our best to win the match"
...............The boys said they had to try their best to win the match.............................
11.Her classmate said"Ha is the most intelligent girl in our class"
..............Her classmate said Ha was the most intelligent girl in their class...................
12.The car is uncomfortable,so I don't buy it.
If.................the car were comfortable, I would buy it.....................
13.They can't travel across this desert.
They wish..................they could travel across the desert.................
14."Please repeat what you have said,Mr Binh"Tim said
..........Tim asked Mr Binh to repeat what he had said.........