Just to clarify, it sounds like you're saying that A1 contains not a number but a character string "0.1, 1.5, '0.5, '1.2". Is that right?

If so, you can get Excel to split the character string up into individual numbers and then add the numbers together. But the SUM function, if you use it at all, won't come in until the very end. First you have to explain to Excel how to break up the string into pieces. Do you want to continue?