1
general::
Draw the proper inference from existing evidence, as in Putting two and two together, it's not hard to guess who will be chosen for the lead role in the play. [Mid-1800s]
American Heritage Idioms
2
general::
Phrase(s): put two and two together
to figure something out from the information available. • Well, I put two and two together and came up with an idea of who did it. • Don’t worry. John won’t figure it out. He can’t put two and two together.
McGrawhill's American Idioms And Phrasal Verbs