bonjour
577 = x * 20 + 10
577 = 20 x + 10
577 - 10 = 20 x
567 = 20 x
x = 28.35
577 : 28.35 = 20 et reste 10
aîné = x
cadet = x/2
jeune = ( x /2) : 3
x + x /2 + ( x /2) : 3 = 280
x + x/2 + x/2 x 1/3 = 280
x + x /2 + x /6 = 280
6 x /6 + 3 x /6 + x /6 = 1680/6
10 x = 1680
x = 168
aîné = 168 €
cadet = 168 : 2 = 84 €
jeune = 84 : 3 = 28 €
