Decimals

This is what I've learnt about decimals.

I've learnt that 0.3+0.8=1.1 and 3+2=5 so the answer would be 1.1+5=6.1. Now I'm gonna tell you what I know about decimals. I know that 

10 tenths make a whole

10 hundredths make a whole

1000 thousandths make a whole.

Something I found challenging was trying to solve decimals.