faut simplifié : 42/15 × 9/12 =

[tex] \frac{42}{15} * \frac{9}{12} = \frac{3*14}{3*5} * \frac{3*3}{3*4} = \frac{14}{5} * \frac{3}{4} = \frac{14*3}{5*4} = \frac{42}{20} = \frac{2*21}{2*10} = \frac{21}{10} [/tex]

42/15 x 9/12 = 378/180 = 18 x 21 / 18 x 10 = 21/10