Bonjour,
[tex] \frac{a + b + c}{3} = \frac{5}{12} [/tex]
[tex] \frac{4a + 4b + 4c}{12} = \frac{5}{12} [/tex]
[tex]4 \times \frac{1}{4} +4 \times \frac{1}{2} + 4c = 5[/tex]
[tex]1 + 2 + 4c = 5[/tex]
[tex]4c + 3 = 5[/tex]
[tex]4c = 5 - 3[/tex]
[tex]4c = 2[/tex]
[tex]c = \frac{2}{4} = \frac{2 \times 1}{2 \times 2} = \frac{1}{2} [/tex]
