0.9kg ice melts into water, and the volume is reduced by 0.1m3 0.9kg ice melts into water, which reduces the volume by 0.1m3 ...
0.9kg ice = 0.9kg water
Because the density of water is 1000 kg / m3
Then we can get V water = 0.9kg △ 1000kg / m3 = 0.0009m3
The volume of ice is 0.0009m3 + 0.1m3 = 0.1009m3
The density of ice is 0.9kg △ 0.1009m3 ≈ 9kg / m3