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Ngvang
2 năm trước
Một chiếc chìa khóa số có 3 vòng số, mỗi vòng gồm 10 chữ số khác nhau. Khóa chỉ mở được nếu trên cả 3 vòng là các chữ số đúng của nó. Hỏi rằng trong trường hợp tồi nhất ta phải quay bao nhiêu lần? Giả sử mỗi lần quay thử mất 10s. Hỏi cần bao nhiêu thời gian để thử hết các trường hợp.
Thích Trả lời Chia sẻ

Các câu hỏi liên quan

I. Viết lại các câu sau sử dụng cách nói gián tiếp. 1. “Open the door,” he said to them. - He told them................................................................... 2. “Where are you going?” he asked her. - He asked her where......................................................... 3. “Which way did they go?” he asked. - He asked... ...................................................................... 4. “Bring it back if it doesn’t fit”, I said to her. - I told... ............................................................................ 5. “Don’t try to open it now,” she said to us. - She told... ........................................................................ 6. “Is it going to be a fine day today?” I asked her. - I asked her... .................................................................... 7. “He’s not at home”, she said. - She said that... ................................................................. 8. “Is the bus station far away?” the girl asked. - The girl wanted to know... .............................................. 9. “Don’t stay out late, Ann” Tom said. - Tom told Ann... ............................................................... 10. “Please let me borrow your car,” he said to her. - He asked... ........................................................................ 11. “Jean, have you seen my gloves?” Thomas asked. - Thomas asked Jean..... 12. Don’t leave the window open, Mary”, I said. - I told Mary.... ................................................................... 13. “I’ll have a cup of tea with you,” she said. She said that... 14. “I’ll pay him if I can” she said. - She said that... ................................................................... 15. “What are you going to do next summer?” she asked. - She asked us.... ................................................................... 16. “I’ll phone you tomorrow,” he told Jack. - He told Jack that.... ............................................................. 17. “Can I sit beside you, Jean?” Tom asked. - Tom asked Jean.... .............................................................. 18. “I want a camera for my birthday,” he said. - He said that.... ................................................................... 19. “Don’t keep the door locked,” he said to us. - He told us.... ................................................................... 20. “How long are you going to stay?” I asked him. - I asked him ………………….... 21. “Are you going by train?” she asked me. - She wanted to know.... .................................................. 22. “Don’t use too much hot water,” she said to us. - She asked us.... .............................................................. 23. “Will you come to my party?” she said to me. - She invited me.... ............................................................ 24. “Don’t do it again,” she said to them. She told them.................................................................. 25. “ Did Mr Brown send the potatoes to you?” she asked. - She asked....................................................................... 26. “Don’t get your shoes dirty, boys,” she said. - She told.......................................................................... 27. “What do you want for lunch today, Peter?” Mary asked. - Mary asked....................................................................... 28. “Can I borrow your typewriter, Janet?” asked Peter. - Peter asked if ....................................................................... 29. “Why didn’t I get a computer before?” thought the office manager. - The office manager wondered............................................................ 30. “You had better not lend him any more money, Elizabeth,’’ said John. - John advised Elizabeth........................................................................

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