This is a basic mechanic question that I have not seen asked... sorry if it's a stupid question. Here is an example:

I am trying to complete the Adventure Card "Transported By Magic". This card requires you to complete two tasks: 6 Investigation, and 2 Scrolls.

I roll 6 dice, getting 2Inv, 3 Inv, 1Inv, Scroll, Peril, Peril. I place the 2 & 3 &1 Investigation dice on the first task, completing it.

Am I allowed to place the 1 scroll that I did roll on the other task? Since I didn't complete the task (only one task can be completed at a time) am I allowed to do that, then roll the remaining two dice in the hopes that I get the second Scroll I need to complete the second task?

Or do I place the 6 Investigation, then have to take a completely fresh stab at completing the 2 Scroll task with the three remaining dice no matter what?

Sorry, I can't really find anything that clearly states that dice can ONLY be placed on a task to complete that task. Thank you for your help.

Nope. Only one task can be completed at a time (unless your investigator's special ability it to allow more than one be completed). Even if you roll the perfect dice to complete the entire adventure in one roll you may only complete one tast at a time. This also applies to focusing. Even if one of the dice would help you complete another task, you cannot focus that die if you are completeing a different task on that roll. Spells, on the other hand, will allow you to save a die for a future task, but there issome uncertainty on when a spell can be used which will hopefully be clarified when the FAQ comes out.

I understand that only one task may be completed at one time. I guess my question is can I "work on" multiple tasks at a time.

To me they are the same question. The only way you can work on multiple tasks at once is with a spell card. Otherwise, no, you must re-roll any dice not used to complete the first task.

to help clarify, You can never partially complete a line. So the answer to your question is No.

Thank you mike, and thank you both for your input.