How can you write 0.40 in simplest form as a fraction?

0.40 =

0.40/ 1.00

Cancel down by '10'

0.4/1.0

Cancel down the decimal point

04/10

The 'zero' to the left of '4' is trivial, 'drop it'.

Hence

4/10

Cancel down by '2'

2/5

The fraction in its simplest form .