Работу по рытью траншеи примем за единицу (целое).
1) 1 : 3 = 1/3 - часть траншеи, которую выроет рядовой Роев за 1 час;
2) 1 ч 36 мин = 1 ч + 36/60 ч = 1 3/5 ч = 8/5 ч
1 : 8/5 = 1 · 5/8 = 5/8 - часть траншеи, которую выроет рядовой Героев за 1 час;
3) 1/3 + 5/8 = 8/24 + 15/24 = 23/24 - часть траншеи, которую они выроют вместе за 1 час;
4) 4 ч 48 мин = 4 ч + 48/60 ч = 4 4/5 ч = 24/5 ч
1 : 24/5 = 1 · 5/24 = 5/24 - часть траншеи, которую закопает сержант Закопаев за 1 час;
5) 23/24 - 5/24 = 18/24 = 3/4 - часть траншеи, которая останется вырытой за 1 час при совместной работе всех троих;
6) 1 : 3/4 = 1 · 4/3 = 4/3 = 1 1/3 ч - время всей работы.
ответ: через 1 ч 20 мин траншея будет вырыта.
1. She found £10 beneath the sofa.
2. James filled to the police to report the incident.
3. He dived into the swimming pool twice.
4. He told me the truth.
5. I watched the last episode of my favourite TV series yesterday.
6. She sended him a present by post.
7. Mary crying a lot when she heard the bad news.
8. Brian went the train to London.
9. She felt happy when she got her jewels back.
10. Peter dropped my mother's antique vase. It broke into thousands of pieces.
11. Laura сalled her mother as soon as she arrived in Paris.
12. He stoped talking when I walked into the room.
13. She tryed to stop the thief, but he got away.
14. She took the glass with orange juice.
15. Miss Marple solved many mysteries in St Mary Mead.
GOOD LUCK
