Реши устно и заполни пропуски

1. \(2870-50\implies\) [ ] \(+\,180\implies\) [ ] \(:20\implies\) [ ] \(+\,850\implies\) [ ].
2. \(700+1800\implies\) [ ] \(:250\implies\) [ ] \(+\,25\implies\) [ ] \(\cdot\,8\implies\) [ ].
3. \(2400:600\implies\) [ ] \(\cdot\,310\implies\) [ ] \(-\,130\implies\) [ ] \(+\,880\implies\) [ ].