Question

determinati numerele de forma abcd cu cifre distincte stiind ca a+d=b+c=5

Answer 1

a=1:
  => d=4
  Daca b=0 => c=5
  Daca b=2 => c=3
  Daca b=3 => c=2
  Daca b=5 => c=0

a=2:
  => d=3
  Daca b=0 => c=5
  Daca b=1 => c=4
  Daca b=4 => c=1
  Daca b=5 => c=0

a=3:
  => d=2
  Daca b=0 => c=5
  Daca b=1 => c=4
  Daca b=4 => c=1
  Daca b=5 => c=0

a=4:
  => d=1
  Daca b=0 => c=4
  Daca b=2 => c=3
  Daca b=3 => c=2
  Daca b=5 => c=0

a=5:
  => d=0
  Daca b=1 => c=4
  Daca b=2 => c=3
  Daca b=3 => c=2
  Daca b=4 => c=1

Deci sunt 5*4=20 astfel de numere (se pot determina prin inlocuirea cifrelor gasite in fiecare caz in parte).