Vì x,y là số tự nhiên nên ta có \(2x+1\ge1\) ; \(y-3\ge-3\)

Từ (2x+1)(y-3) = 10 suy ra các trường hợp :

1. \(\begin{cases}2x+1=1\\y-3=10\end{cases}\)

2. \(\begin{cases}2x+1=2\\y-3=5\end{cases}\)

3. \(\begin{cases}2x+1=5\\y-3=2\end{cases}\)

4. \(\begin{cases}2x+1=10\\y-3=1\end{cases}\)

Vậy có 4 cặp số (x,y) thỏa mãn

(bạn tự liệt kê ra nhé ^^)

1.how OLD are you?-i'm thirteen years old

2.how. TALL are you?-i'm one meter 40 centimeters tall

3.how HIGH Is that building?

4.how HEAVY are you?-i'm 45 kilos

5.how MUCH do you weigh?-nearly 42 kilos

6.how OFTEN do you have a medical check-up?-every six months

7.how MANY students are there in your class?

8.how LONG does it take you to go to school every morning?

9.how FAR is the yard?-it's 40 meters long

10.how WIDE is the river?-it's twenty meters wide

a/

mFe(OH)3 = mFe2O3 + mH2O

x = mFe(OH)3 = mFe2O3 + mH2O = 160 + 54 = 214 (g)

b/ m Chất tham gia = m sản phẩm

A . It's dangerous to go hiking there . You should tell someone where you are going

B : Yes . And I will take a warm coat . It is very cold there

A: Yes and you should take a mobile phone . It's very important.

B: OK , and I will take all necessary things along with me

Tại bài không cho các từ gợi ý nên mình chỉ làm theo cảm tính thôi ^^

Alice is ALWAYS LATE FOR school because she's very slow .

Our parents are busy all day but they always take care OF us.

Miss Hoa is a (1) TEACHER. She teaches at a (2) SMALL school in the country. Every day, she gets up (3) AT half past five. She (4) TAKES a shower and gets dressed. She has breakfast, then she (5) LEAVES the house at a quarter to seven. The school is near (6) HER house, so she walks to school. Classes start at seven and (7) END at half past eleven. After classes, she (8) ? home and has lunch at twelve.

mCuSO4 = 4% x 200 = 8 (g)

=> nCuSO4 = 8/160 = 0,05 (mol)

PTHH : Zn + CuSO4 ------> ZnSO4 + Cu

a/ Từ PTHH ta có nZn = nCuSO4 = 0,05 (mol)

=> mZn = 0,05 x 65 = 3,25 (g)

b/ nZnSO4 = nCuSO4 = 0,05 (mol)

Suy ra mZnSO4 = 0,05 x 161 = 8,05 (g)

Vì Cu là chất kết tủa nên mdd = mZn + mddCuSO4 - mCu

= 3,25 + 200 - 0,05 x 64 = 200,05 (g)

=> C% = 8,05 / 200,05 x 100 = 4,024%

a/ 4P + 5O2 -------------> 2P2O5 (Điều kiện nhiệt độ)

P2O5 : Điphopho pentaoxit

b/ Theo pt ta có nP2O5 = 1/2nP = 0,1 (mol)

=> mP2O5 = 0,1 x 142 = 14,2 (g)

Mà thực tế thì mP2O5 = 14 (g)

Vậy tỉ lệ hao hụt : \(100\%-\frac{14}{14,2}.100=1,408\text{%}\)

c/ nP2O5 = 28,4 / 142 = 0,2 (mol)

Theo pthh : nO2 = 5/2nP2O5 = 0,5 (mol)

=> mO2 = 0,5 x 32 = 16 (g)

mMgCO3 = 200 - 200x5% = 190 (g)

nMgCO3 = 190/84 = 95/42 (mol)

PTHH : MgCO3 ----------> MgO + CO2

95/42 95/42 95/42

=> nMgO = nCO2 = nMgCO3 = 95/42 (mol)

=> mMgO = 95/42 x 40 = 90,476 (g)

mCO2 = 95/42 x 44 = 99,524 (g)