Definition
To infer or deduce the truth or conclusion about a situation based on the available information or evidence.
She noticed he was coming home late more often and his text messages became secretive, so she put two and two together and guessed he might be having an affair.
When I saw him having lunch with the new colleague frequently, I put two and two together and suspected there might be something going on between them.
He put her recent unusual behavior together with her hushed phone calls with a new colleague and quickly realized she was about to quit her job.