Interesting intelligence problem (second grade Olympic mathematics)
1, half covered on the sixth day. Because the seventh day is all.
2. First put 7 kg of water in the vat, and then fill the 5 kg bucket with water, so there are 2 kg left in the 7 kg bucket. Pour this 2 kg into a 9 kg bucket and then into a 7 kg bucket of raw water, and it will be 9 kg.