Gọi tuổi con và tuổi mẹ lần lượt là x, y (\(x,y\inℕ^∗\))

Theo đề, tuổi con hiện nay là x =\(\frac{1}{5}\)y  (1)

Tổng tuổi của mẹ và con sau 3 năm nữa là (x + 3) + (y + 3) = 42 <=> x + 3 + y + 3 = 42 <=> x + y + 6 = 42 <=> x + y = 42 - 6 <=> x + y = 36  (2)

Từ (1)(2) ta có hpt

\(\hept{\begin{cases}x=\frac{1}{5}y\\x+y=36\end{cases}\Leftrightarrow}\hept{\begin{cases}x=\frac{1}{5}y\\\frac{1}{5}y+y=36\end{cases}\Leftrightarrow}\hept{\begin{cases}x=\frac{1}{5}y\\\frac{6}{5}y=36\end{cases}\Leftrightarrow}\hept{\begin{cases}x=\frac{1}{5}y\\y=36\div\frac{6}{5}\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}x=\frac{1}{5}y\\y=30\end{cases}\Leftrightarrow}\hept{\begin{cases}x=\frac{1}{5}.30\\y=30\end{cases}\Leftrightarrow}\hept{\begin{cases}x=6\\y=30\end{cases}}\)(TMĐK)

Vậy tuổi con hiện nay là 6 tuổi, mẹ là 30 tuổi

\(5\cdot5\cdot\left(630-315\cdot2\right)\)

\(=5\cdot5\cdot\left(630-630\right)\)

\(=5\cdot5\cdot0=0\)
 

Sắp xếp lại câu

1. some songs/to make their father happy/have parties/they can also/ ,read poems or sing

->they can also have parties, ,read poems or sing some songs to make their father happy

2. they/in Vietnam/ enjoy/ although many tourists / don't understand/ most of the festivals/ from aboard/ Vietnamese culture

->

3. can see/ laterns/ the city/ all over/ You/ thousands of.

-> You can see lanterns all over the city thousands of.

4. Britney and Lola,/ the/ they/ however, mentionned/ dressing/ pracing/ in/ were/ room.

->Britney and Lola , however mentioned , they were practising dressing in the room.

5. about the eruption/ because the scientist/ were saved/ thousands of people/ had warned them

->thousands of people were saved because the scientist had warned them about the eruption

6. the earthquake./ damaged/ Almost/ was/ all of my house/ by

->Almost all of my house was damaged by the earthquake.

7. disasters./ More trees/ should be/ to prevent/ some natural/ planted

->More trees should be planted to prevent some natural disasters.

8. to hurricanes./ to give names/ The people/ are/ the first/ in Puerto Rico

->The people in Puerto Rico are the first to give names to hurricanes.

9. rained/ Though/ went/ we/ it/ heavily/ school/ to/ time/ on.

->Though it rained heavily, we went to school on time.

\(1\frac{1}{3}.1\frac{1}{8}.1\frac{1}{15}....1\frac{1}{9800}=\frac{4}{3}.\frac{9}{8}.\frac{16}{15}....\frac{9801}{9800}\)

\(=\frac{2.2}{1.3}.\frac{3.3}{2.4}.\frac{4.4}{3.5}....\frac{99.99}{98.100}\)

\(=\frac{2.3.4...99}{1.2.3....98}.\frac{2.3.4...99}{3.4.5...100}\)

\(=99.\frac{2}{100}=99.\frac{1}{50}=\frac{99}{50}\)

aweee tks <3

1.Did Minh go

2.goes

3,have leant

4.have visited

5.reach