Рассмотрим некоторое число n, например, 12. если оно не является палиндромом (число, которое одинаково читается слева и справа), то к нему прибавляется его перевёрнутая копия: 12 + 21 = 33. за один шаг получили палиндром. число 28 превращается в палиндром за 2 шага: 28+82 = 110, 110+011=121. найдите наименьшее число, которое превращается в палиндром за а) 2 шага, б) 3 шага?

Пускай скорость пассажирского поезда будет х км/ч. Тогда скорость товарного поезда будет х-20 км/ч. Время, за которое пассажирский поезд пройдёт 480 км, пусть будет у ч, тогда время товарного поезда будет у+4 ч. Имеем систему уравнений: х×у=480, (х-20)×(у+4)=480. х=480/у, ((480/у)-20)×(у+4)=480, ((480-20у)/у)×(у+4)=480, (480-20у)×(у+4)=480у, 480у+1920-20у^2-80у=480у, -20у^2-80у+1920=0, -у^2-4у+96=0, D=(-4)^2-4×(-1)×96=16+384=400, у1=(4-корень с 400)/(2×(-1))=(4-20)/(-2)=(-16)/(-2)=8, у2=(4+корень с 400)/(2×(-1))=(4+20)/(-2)=24/(-2)=-12. у2=-12 - не может быть ответом задачи, так как время не может быть отрицательным. Значит у=8, х=480/8=60. Имеем: скорость пассажирского поезда равна 60 км/ч, скорость товарно поезда равна 60-20=40 км/ч.

Добрый день. Я так понял на экспедицию? Если да, то вот примерное сочинение.
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Hiking TripПоходI like hiking a lot. In my opinion, it’s a great source of pleasure and health benefit. Hiking is very similar to a walking tour or camping. It is a long walk in the countryside with occasional stops. Most people go hiking for pleasure or physical fitness. It is important from time to time to leave crowded cities and go out for a walking tour. The open air has a bracing effect on our minds. The sight of huge trees and green bushes, blooming wild flowers and running streams, the birds’ singing – it all carries us away from the depressing daily routine. I especially like hiking in mountainous areas. It is more thrilling that walking in the plains. Last time we went hiking was in summer. Together with our teacher and a group of school children we went to find some picturesque places on the bank of the River Don. We took all the necessary items, including sleeping bags, some food, first aid kit and mosquito spray. We wore sporty outfit and comfy boots. Our rucksacks were rather heavy, but it didn’t spoil our journey. Most importantly we chose the route of our journey and fully planned the trip. We set out early in morning. Luckily, the weather was perfect. Although, there were some clouds in the sky, the wind soon took them away. Our first meal in the open air felt fantastic. We baked some potatoes and frankfurters. It was rather hot, so we could sunbathe and swim in the river. We also played some outdoor games, such as volleyball and football. The next morning we went fishing. It was a great fun. While hiking, we saw lots of beautiful places. Time passed so quickly and soon we had to go back home. No one wanted to leave. We thought it was an unforgettable experience.