Maths Guru
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PuzzleAges 5–11Part of Arcade Walk

Kakuro: the cross-sums number crossword

Kakuro, also called Cross Sums, is a number crossword. Children fill every white cell with a digit from 1 to 9 so that each run of cells adds up to the clue that labels it, without repeating a digit within a run. It is excellent practice for number bonds and addition.

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Kakuro

How to play

  1. Fill every white cell with a digit from 1 to 9.
  2. Each black clue cell shows two sums split by a diagonal: the top-left number is the down sum for the cells below it, and the bottom-right number is the across sum for the cells to its right.
  3. Within a run, every digit must be different.
  4. Start with the smallest or largest sums. A 2-cell sum of 3 can only be 1+2, and a 2-cell sum of 17 can only be 8+9.
  5. Use Check Answers when you are ready. You get 3 checks.

Maths skills it builds

  • Number bonds and addition
  • Combinations of digits
  • Logical deduction
  • Elimination

Why it works

Kakuro practises addition facts in the most useful way: by asking which sets of digits can make a given total. Children quickly learn that some totals have only one possible combination and use that as a foothold. The 6×6, 8×8 and 10×10 sizes give a steady ramp.

Related maths skills

Questions parents ask

How do clue cells work?

In Maths Guru's Kakuro, the number at the top-left of a black cell is the sum down for the white cells below it, and the bottom-right number is the sum across for the white cells to its right.

What sizes are there?

6×6 for Beginner, 8×8 for Explorer and 10×10 for Champion.

Can digits repeat?

Not within the same run. The same digit can appear in different runs.

Can guests play?

Yes. Guests can play the Beginner level. Signing up unlocks Explorer and Champion.

Kakuro

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