What is the additive and multiplicative inverse of 0.4?

The answers are: ##-0.4and2.5##

The inverse of 0.4 in the additive operation is that element (##a##) that added to 0.4 gives 0.

So:

##0.4+a=0rArra=-0.4##

The inverse of 0.4 in the multiplicative operation is that element (##a##) that multiplied to 0.4 gives 1.

So:

##0.4*a=1rArr4/10a=1rArr2/5a=1rArra=5/2=2.5##.