put two and two together, v. phr.
To figure something out, to understand what really happened. To look at facts and come to a conclusion. This idiom refers to simple math. A similar idiom is two and two make(s) four, which means a statement is obvious or cannot be disputed. This second idiom was recorded as early as 1695.
• It didn’t take long for the police to put two and two together, and they soon arrested the robber.
• You know he’ll put two and two together before too long.
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