calculs relatifs , des ecritures fractionnaires

5/11 * 8/7 : 15/22
= 5/11 * 8/7 * 22/15
= (5 * 8 * 22)/(11 * 7 * 15)
= 880/1155
= (55*16)/(55*21)
= 16/21

9/5 * 7/8 - 3/4 : 5/7
= (9 * 7)/(5 * 8) - 3/4 * 7/5
= 63/40 - (3 * 7)/(4 * 5)
= 63/40 - 21/20
= 63/40 - (21 * 2)/(20 * 2)
= 63/40 - 42/40
= (63 - 42)/40
= 21/40

c tres facile regarde les otre