Kali family used 45.505 litres of water in April. They used 910 millilitres less water in May than in april. How much water did they use in April and May altogether? Express the answer in litres and millilitres.
In April, Kali's family used 45.505 liters of water.
In May, they used 910 ml less water than in April, which is equivalent to 910/1000 = 0.91 liters.
So, they used 45.505 - 0.91 = 44.595 liters of water in May.
Therefore, they used a total of 45.505 + 44.595 = <<45.505+44.595=90.1>>90.1 liters of water in April and May altogether.
Since there are 1 liter = 1000 ml, then 0.1 liters = 0.1 x 1000 = <<0.1*1000=100>>100 ml.
Hence, they used a total of 90.1 liters = <<90.1=90.1>>90.1 liters = 90 liters and 100 ml in April and May altogether. Answer: \boxed{90\text{ liters } 100\text{ ml}}.