Vì thời gian để đoàn tàu chui qua đường hầm = thời gian vượt qua cột điện + thời gian đi được chiều dài đường hầm

Thời gian để tàu đi qua được 260 m là :

    1 phút - 8 giây = 52 giây

Vận tốc của đoàn tàu là :

    260 : 52 = 5 ( m/giây )

Chiều dài đoàn tàu là :

    5 x 8 = 40 ( m )

         Đáp số : 40 m ; 18 km/giờ

Số nhân với 74 là:

  2695:(7+4)=245

Tích đúng là:

  245x74=18130

       Đ/S:18130

k nha mình là người đầu tiên đó nha

Ex1: Complete the sentences.Use the present perfect form of the verbs in brackets

a.I .....'ve lived.....here since 1989(live)

b.They........'ve worked.......... for his factory for 20 years(work)

c.He...'s read... this novel three times (read)

d Hoa and me.......'ve known.......each other we were at the same class(know)

e.I....'ve seen.... her since last evening(see)

f.John.....has been........in England since yesterday(be)

Ex2: Complete the sentences .Put for and since in each group

1.She has been in Vung Tau.....since.....January

2.Ha and Nam have seen this film...since.......7 o'clock

3.I have send her 3 letters ...since........last week

4.My sister has worked at that hospital...for.....5 years

5.I have known her.........since....... we were at alementary school

1. Wher are you( be), nam

- I am here. I ( read)am reading in my room

2. Look! The plane ( fly)is flying towards the airport. It ( land)is going to land

3. What about ( go)going the cafeteria?

6. My mother wants me( buy)to buy two kilos of potatoes

7. How many floors does your school ( have)have?

8. Your should ( do)domorning exercise