Réponse :

Explications étape par étape :

1) c = 5

Moyenne pondérée = (5 x 1,5 + 12 x 4 +15 x 2 + 5x)/(1,5 + 4 + 2 + 5) = 22

→ (85,5 + 5x)/12,5 = 22

→ 85,5 + 5x = 22 x 12,5 = 275

→ 5x = 275 - 85,5 = 189,5

→ x = 189,5/5 = 37,9

2)

x = 36

Moyenne = (5 x 1,5 + 12 x 4 +15 x 2 + 36c)/(1,5 + 4 + 2 + c) = 20,625

→ (85,5 + 36c)/(7,5 + c) = 20,625

→ 85,5 + 36c = 20,625(7,5 + c)

→ 85,5 + 36c = 20,625 x 7,5 + 20,625 c = 154,6875 + 20,625 c

→ 36c - 20,625c = 154,6875 - 85,5

→ 15,375c = 69,1875

→ c = 69,1875/15,375

→ c = 4,5