a) Dãy số trên có số số hạng là:

(390-5):5+1=78(số)

Tổng là:

(390+5)x78:2=15405

Đáp số: 15405

b) Dãy trên có số số hạng là:

(100-1):1+1=100(số)

Tổng là:

(100+1)x100:2=5050

Đáp số: 5050

tk nhé

a, Dãy số này cách nhau 5 đơn vị

Tổng dãy số trên là : 

(5 + 390) x ((390 - 5 ) : 5 + 1) : 2 = 15405

b, Dãy số cách đều nha 1 đơn vị

Tổng dãy số là : 

(1 + 100) x ((100 - 1) : 1 + 1) : 2 = 5050

bn  nhớ tick cho mình nha 

7a 

bn ko chụp câu 8

9a

10c

11b

12d

13a

1 plays

2 are reading

3 sing

4 do - do, help

5 is teaching

7 visited

8 doesn't like

9 watch

10 gets - has - brushes - goes - has

11 played - was

12 met

13 are going to have

14 did - do , planted

15 didn't come

16 paint

17 taught

18 have never been

19 takes

20 have - had 

21 received

22 is going to invite

23 is waiting

24 talked

25 is going to travel

26 went - didn't buy

27 doesn't learn - will fail

28 washes

29 will be - watches

30 will phone

2 are reading

3 sings

4 do - do - help

5 is teaching

7 visited 

8 doesn't like

9 watch

10 gets - has

6. 10 brushes - goes

6. 30 has

11 played - was

12 met

13 will have

14 did - do - planted

15 didn't come

16 paint

17 taught

1 plays

2 are reading

3 sing

4 do - do, help

5 is teaching

7 visited

8 doesn't like

9 watch

10 gets - has - brushes - goes - has

11 played - was

12 met

13 are going to have

14 did - do , planted

15 didn't come

16 paint

17 taught

18 have never been

19 takes

20 have - had 

21 received

22 is going to invite

23 is waiting

24 talked

25 is going to travel

26 went - didn't buy

27 doesn't learn - will fail

28 washes

29 will be - watches

30 will phone

1.The stomachache prevented Mr.Thanh from enjoying the meal.

2.Mrs.Oanh is a good cook.

3.You don't have to finish all the work today.

4.He drives slower and more careful than I do.

5.It takes the boy 3 hours a day to learn the lesson.

6.He liked oranges than durians.

7.One of the greatest football player in the world is Zidane.

8.Why were you absent from class last Monday?

9.The exam was not difficult as we thought.

10.The visitor spoke too quick for me to understand what he said.

bài gì?

bài vật lí

bài gì vậy? chẳng có đầu đuôi

1. A

2. B

3. D

4. A

5. C

1 - A

2 - B

3 - D

4 - A

5 - C

8x = 7,8x + 25

8x - 7,8x = 25

(8 - 7,8)x = 25

0,2x = 25

     x = 25 : 0,2

     x = 125

x(8-7,8)=25

   x0.2  = 25

   x       = 25:0.2

   x       = 50

8x = 7,8x + 25

8x - 7,8x = 25

1,5x = 25

x = \(\frac{25}{1,5}\)

x = \(\frac{50}{3}\)

Bài 1

1/ D

2/ A

3/ D

4/ A

5/ A

\(\frac{3}{x+5}=15\%\)

\(\frac{3}{x+5}=\frac{15}{100}\)

\(\frac{3}{x+5}=\frac{3}{20}\)

\(\Rightarrow x+5=20\)

\(\Rightarrow x=20-5\)

\(\Rightarrow x=15\)

~ Thiên mã ~

\(\frac{3}{x}+5=15\%\)

\(\frac{3}{x}+5=\frac{3}{20}\)

\(\frac{3}{x}=\frac{3}{20}-5\)

\(\frac{3}{x}=\frac{-97}{20}\)

\(\Rightarrow\left(-97\right)x=3.20\)

\(\Rightarrow\left(-97\right)x=60\)

\(\Rightarrow x=60:\left(-97\right)\)

\(\Rightarrow x=\frac{-60}{97}\)

~ Hok tốt ~

\(\frac{3}{X}\)+5=\(\frac{15}{100}\)

\(\frac{3}{X}\)+5=\(\frac{3}{20}\)

\(\frac{3}{X}\)=\(\frac{3}{20}\)-5

\(\frac{3}{X}\)=\(-\frac{97}{20}\)

X=\(-\frac{97}{20}\)\(:\)3

X=\(-\frac{97}{60}\)