Gọi CTHH của phân tử là: \(Na_2CO_3.nH_2O\)

Theo đề, ta có: \(\dfrac{106}{106+18n}.100\%=37,07\%\)

\(\Leftrightarrow n\approx10\)

Vậy CTHH của phân tử là: Na₂CO₃.10H₂O

Chọn C

Life is much better than in the past.Obiously,there are a lot of differences between the life in the past and life nowadays

First of all,the life nowadays is more modern.In the past,people didn't have electricity.there are a few people having the television and every evening the people in the village came to their house to watch TV.Besides,there are many modern equipments,today,such as: mobile phone,computers,ipads,...

Secondly,the life is becoming more convenient.We can buy everything we want which is useful without going out.

However,the life is less sensitive.In modern life,people don't have much time together because they are busy with their work.It means that people become less friendly.Moreover,the cost of living is more and more expensive.In addition,the life is more modern,as a result,the environment become more and more polluted.

In conclusion,life has been changed so much nowadays.There are a lot of bad things and goods thing.As a Vietnamese,we have to try our best to develop our country and minimize the bad things in modern life :3

~Good luck!!

11 * 22 * 33 * 44 * 55 * 66 * 77 * 88 * 99 = ( Kết quả 1 ) 855652058110080

                                                                   ( Kết quả 2 ) ~ 8,5565205811008 x 10¹⁴

Đề bài sai hả bạn

ko pạn à~

=4 tuổi

Câu 4: 

1) Ta có: \(A=99\cdot101\)

\(\Leftrightarrow A=\left(100-1\right)\left(100+1\right)\)

\(\Leftrightarrow A=100^2-1\)

mà \(B=100^2\)

nên A<B

program 06;
Uses crt;
Var
  T:real
  i;n:integer;
Begin
clrscr;
 write('n=1');Readln(n);
 T:=06
 for i:=1 to n do
  T:=\frac{1}{1}.2+\frac{1}{2}.5+\frac{1}{3}.8+\frac{1}{4}.11
 write('T=06' T);
 readln;
 end.

C gửi bài nà! Tích cho c nha!b2:b3:b4: