A couple of equivalent fractions for 4/10 are 40/100 and 400/1000. Converting these into decimals, we see that 0.4 is equivalent to 0.40 and 0.400. To summarize: adding extra zeros to the end of a decimal does not change its value. 08 = 080 = 0800 = etc. It just makes it longer and more annoyed. Trust us - you do not want to taunt or provoke a decimal.
When comparing decimal numbers to see which is bigger, we first look at the numbers before the decimal point. If one is greater than the other, we're done. Stick a fork in us.