giúp mik vs Một người đi được quãng đường s1 hết thời gian t1 giây, đi quãng đường s2 hết thời gian t2 giây. Vận tốc trung bình của người này trên cả hai quãng đường s­1 và s2 là A: vtb = s1/t1 + s2/t2 B: vtb = (s1 + s2) / (t1 + t2) C: vtb = (t1 + t2) / (s1 + s2) D: vtb = (v1 + v2) / 2

Các câu hỏi liên quan

IHãy cho biết tính từ so sánh hơn và nhất của từ (new) Comparatives:................................. Superlatives:................................. IIChia động từ trong ngoặc ở dạng đúng 1You must (be)………………… careful. 2We (visit)…………………… our grandparents tomorrow. III.Đọc kỹ đoạn văn sau rồi trả lời các câu hỏi ở bên dưới(2 điểm) Yesterday was Hoa’s thirteenth birthday. She had a small party with her friends. They ate a lot of food, fruits and cakes. In the evening , Hoa had a stomachache. Her aunt was worried. She called a doctor. The doctor arrived and gave Hoa some medicine. She took the medicine and went to bed . Today, Hoa feels better. 1.When was Hoa’s thirteenth birthday? =>………………………………………………. 2.Why did Hoa have a stomachache? =>………………………………………………. 3.Was her aunt worried? =>………………………………………………. 4.Does Hoa feel better today? =>………………………………………………. IV.Viết lại những câu sau sao cho nghĩa không đổi(2 điểm) 1. Let’s go to the movies. => What about……………………………………….? 2. He is a safe cyclist. =>He cycles………………………………………….. 3. How much does the green dress cost ? => How much ………………………………………….? 4. Lan is taller than her sister => Lan’s sister is ……………………………………………? V.Viết câu hỏi cho các từ gạch dưới trong các câu sau. 1. I went to bed at 11 o'clock last night. => ......................................................................................................... 2. She bought that dictionary because she didn't know many English words. => ......................................................................................................... 3. I sent these letters to my pen pal in Canada. => ......................................................................................................... 4. Lan went to Nha Trang last month. => ......................................................................................................... 5. She went to Nha Trang by train. => ......................................................................................................... 6. They saw many types of fish and turtles in the aquarium. => ......................................................................................................... 7. I ate bread and eggs for breakfast this morning. => ......................................................................................................... 8. They were in the countryside last summer. => ......................................................................................................... VII. Sắp xếp các từ sau để thành câu hoàn chỉnh. 1. short/ stopped/ the/ they/ at/my restaurant/ for/ time/ a. => ....................................................................................................... 2. bought/ made/ mother/ dress/ material/ my/ and/ me/ the/ a/ for. => ......................................................................................................... 3. apartment/ door/ mine/ they/ an/ to/ rented/ next. => ......................................................................................................... 4. first/ saw/ shark/ time/ she/ this/ the/ a / is. => ......................................................................................................... 5. wrote/ often/ year/ letters/ pen pal/ to/I / my/ last. => ......................................................................................................... 6. taught/ some/ she/ friends/ her/ Vietnamese. => ......................................................................................................... 7. summer/ visit/ you/ Hanoi/ last/ did/ vacation? => .......................................................................................................