I'm trying to help my daughter with her math homework. There's a problem:

Règle effacée
Des nombres et des traits ont été effacés sur cette règle:
[ an image of a ruler with measures 0, 2, 5, 9, 11 and 12; other have been erased ]
en utilisant cette règle sans la compléter, quelles longueurs pourrait-on mesurer en une fois ?
Justifie ta réponse.

What does "mesurer en une fois" mean in this context?

1 Answer 1


It means: What length can you measure in only one attempt?

Exemple, you have a "clean" ruler (20cm, with all the measures between it start and end) and a line to measure (> 20cm)You can measure the "first" 20cm "put" your finger, and start checking the length from your finger, add the two values. So that's 2 attempts at least.

From your maths problems, the simplest values to find are: (0,) 2, 5, 9, 11 and 12. But in fact, you can also measure 3 (starting point at 2, end at 5), 4 (5;9), etc.

  • 3
    Although your answer’s great (+1), especially how it covers all the possibilities, perhaps “operation” would work a little bit better than “attempt” “…. in a single/[in only one] operation.”
    – Papa Poule
    Commented Jun 15, 2015 at 15:00

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