In case anyone needs elaboration of stage2
After taking out 1L of spirit and pouring 1L of water in stage 1, the ratio of spirit:water becomes 9:1.
So in 10L of mixture, 9L of Spirit and 1L of Water.
Similarly, in 1L of mixture, 9/10L=0.9L of Spirit and 0.1L of water will be there.
Now at this stage we are taking out 1L of mixture (containing 0.9L of spirit and 0.1L of water) and in the bucket there is 9L left of which 9*0.9L=8.1L is spirit and 9*0.1L=0.9L of water is there.
Adding 1L of water to this.
Spirit volume remains 8.1L and water becomes 0.9L+1L=1.9L.