Răspuns: 15 banci si 21 elevi
Explicație pas cu pas:
Notez cu ,,b" = banca
1 × b + 6 = 2 × ( b - 4 - 1 ) + 1
2 × ( b - 5 ) + 1 = b + 6
2 × b - 10 + 1 = b + 6
2 × b - b = 6 + 9
b = 15 ( banci )
15 × 1 + 6 = 21 elevi
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Verific: 2 × ( 15 - 4 - 1 ) + 1 = 2 × 10 + 1 = 21 elevi