nerdle

Nerdle #585 Answer

Sunday, August 27, 2023

31+47=78
Structure
AB+CD=EF
Type
Double-Digit Addition
Result
78

How the clues would have read

  • Today's equation begins with a two-digit number in the 30s.
  • This puzzle uses addition only.
  • The result is a 2-digit even number.

The numbers behind it

  • Divisibility: 31 is prime, 47 is prime, and 78 is divisible by 2, 3, 6, 13, 26, and 39
  • Digital roots: 31 → 3+1 = 4, 47 → 4+7 = 11 → 2, 78 → 7+8 = 15 → 6
  • Prime factorization: 31 = 31, 47 = 47, 78 = 2×3×13

Why the structure matters

This puzzle's shape is AB+CD=EF — a double-digit addition, where each letter stands for one digit. Recognising the shape before the arithmetic is what separates a three-guess solve from a six-guess struggle: once you know the equation is a double-digit addition, most of the search space is gone before you have spent a single guess.

The result, 78, factors as 2×3×13 — those factors are exactly the operations that could have produced it.

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