My recent winter holidays were a lot of fun. I tried to visit as many places as I could and to do a lot of different things. Even though the weather wasn't very nice, it didn't make me feel sad. I went to the mall and to the skating-rink with my family and friends. It's always interesting to learn something new, so I also visited the movies and watched some great films. And then, of course, there were New Year and Christmas, which are both my favourite holidays. We had a gorgeous Christmas-tree decorated with toys and Christmas lights. On the first day of new year I got many presents from my family and relatives. After all, it was just great to take some time off from school and to sleep till noon. I really enjoyed my winter holidays.
скорость лодки по течению реки= собственная скорость+скорость течения реки;
скорость лодки против течения реки=собственная скорость-скорость течения реки.
Пусть х км/ч это собственная скорость лодки. Тогда лодка по течению реки проплыла путь равный (х+1,8)*3,5 км, а против течения реки путь равный (х-1,8)*2,5 км. Весь путь равен 49,8 км.
Составим уравнение:
(х+1,8)*3,5+(х-1,8)*2,5=49,8
3,5х+6,3+2,5-4,5=49,8
6х+1,8=49,8
6х=49,8-1,8
х=8 (км/ч) собственная скорость лодки.
24+(-9)=15
-11+13=2
67+(-83)=-16
-34+9=-25
17+(-2)=15
-4+(-5)=9
-63+(-37)=-100
-8+(-5)=-13
-56+6=-50