1. Lena didn't want to get up,did she? Yes, Lena didn't want to get up. 2. Lena had a lot to do, didn't she ? Yes she did. Lena had a lot to do. 3. It was windy and cold outside, wasn't it? Yes it was. It was windy and cold outside. 4. Lena couldn't think about the party and the cake, could she? Yes she couldn't think about the party and the cake. 5. Lena and her mother decided to have lemon tea and sandwiches for breakfast, didn't they ? Yes they did. They decided to have lemon tea and sandwiches for breakfast. 6 Lena was happy to stay in bed, wasn't she? Yes, she was. She was happy to stay in bed.
Пусть х км/ч - собственная скорость катера. Тогда скорость катера по течению - (х+2) км/ч, против течения (х-2) км/ч. Катер был в пути 19 ч-15ч = 4 ч. Из них 2 ч стоял, т. е. катер плыл 4-2=2 ч. Против течения катер плыл 7/(х-2) часов, по течению плыл 27/(х+2) ч. Составляем уравнение: 7/(х-2) + 27/(х+2) = 2 7*(х+2) + 27(х-2) = 2 (х+2)*(х-2) 7х+14+27х-54=2х(квадрат)-8 34х-40-2хквадрат+ 8 =0 2хквадрат -34х + 32=0 хквадрат - 17х + 16 =0 D=17*17-4*16=289-64=225 х1=(17-15)/2 = 1 (км/ч) - не может быть решением данной задачи, т. к. 1 км/ч меньше 2 км/ч, а скорость катера не может быть меньше скорости течения.
2. Lena had a lot to do, didn't she ? Yes she did. Lena had a lot to do.
3. It was windy and cold outside, wasn't it? Yes it was. It was windy and cold outside.
4. Lena couldn't think about the party and the cake, could she? Yes she couldn't think about the party and the cake.
5. Lena and her mother decided to have lemon tea and sandwiches for breakfast, didn't they ? Yes they did. They decided to have lemon tea and sandwiches for breakfast.
6 Lena was happy to stay in bed, wasn't she? Yes, she was. She was happy to stay in bed.