1 .7+(5)+(3.27) ?
In the addition of decimals, each place value is defined by its position in the number.
Why would we want to change these numbers, which are all the same format, into another format?
Just add these as decimals, keeping the decimal points under each other so that the same place values are all aligned.
It might help to add in zeros to allow each number to have the same number of decimal places.