Problema (nível 1): Num tabuleiro $3\times 3$, a Rita quer colocar um algarismo de $1$ a $9$ em cada casa, de modo que sejam todos diferentes e que a soma dos números em cada um das regiões assinaladas seja $20$. (image1) (image2) (image3) (image4) A Rita já colocou os algarismos $3$ e $5$, como na figura seguinte. Indica todas as formas possíveis de a Rita completar o tabuleiro. (image5)


Conteúdo referenciado:
[image1]
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[image2]
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[image3]
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[image4]
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[image5]
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Resolução: As únicas formas de completar o quadrado de modo que a soma do canto inferior direito seja $20$ usam os algarismos $4$ e $8$, logo são: (image6) ou (image7) No primeiro caso, os algarismos que faltam no canto inferior esquerdo são o $2$ eo $9$, e no segundo caso são o $1$ e o $6$. Logo temos as possibilidades: (image8) (image9) (image10) (image11) O primeiro caso é impossível porque no canto superior esquerdo seria necessário usar um $8$ ou um $9$. O quarto caso é impossível porque no canto superior esquerdo seria necessário usar um $4$ ou um $5$. Os restantes casos são possíveis e dão origem às duas possibilidades seguintes: (image12) (image13)


Conteúdo referenciado:
[image6]
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[image7]
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[image8]
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[image9]
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[image10]
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[image11]
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[image12]
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[image13]
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