Răspuns: 25 banci si 29 elevi
Explicație pas cu pas:
Notez numarul bancilor cu ,,b"
2 × ( b - 1 - 10 ) + 1 → elevi
3 × ( b - 15 - 1 ) + 2 → elevi
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3 × ( b - 16 ) + 2 = 2 × ( b - 11 ) + 1 → elevi
3 × b - 48 + 2 = 2 × b - 22 + 1
3 × b - 2 × b = - 21 + 46
b = 25 ( banci )
2 × ( 25 - 1 - 10 ) + 1 = 2 × 14 + 1 = 29 elevi
sau:
3 × ( 25 - 15 - 1 ) + 2 = 3 × 9 + 2 = 29 elevi