Bonsoir,
On a d'une part,
(15/6) * (7/25) = (15 * 7) / (6 * 25) = (3 * 5 * 7) / (2 * 3 * 5 * 5) = 7 / (2 * 5) = 7/10
Et d'autre part 7/2 = (7 * 5) / (2 * 5) = 35 / 10
D'où
7/2 + (15/6) * (7/25) = 35/10 + 7/10 = (35 + 7) / 10 = 42/10 = (21 * 2) / (5 * 2) = 21/5
