Question

Determina cate numere naturale de doua cifre contin cel putin o cifra impara.

Answer 1

Numere impare de 2 cifre: 11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,49,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,81,83,85,87,89,91,93,95,97,99.

În total sunt 45 de numere...

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Answer 2

nr de forma ab cu a∈{1,3,5,7,9}, b∈{0,1...9} sau a∈{1,2,...9}, b∈{1,3,5,7,9}
nr sunt 10,11,12,13,.......19..........10 nr
             21,23,25,27,29.................5 nr
             30,31,32,33,......39...........10 nr
             41,43,45,47,49..................5 nr
             50,51...................59..........10 nr
              61,63,65,67,69.................5 nr
            70,71,72,..............79...........10 nr
              81,83,85,87,89..................5 nr
             90,91,92,93,.........99...........10 nr
nr de nr= 5*10+4*5=50+20=70