Calculs en écriture fractionnaire A) -5÷7+5÷21×9÷25 B) 25÷17÷15÷4-11÷3 C) 5÷4 - 2÷5 × 10÷3

A) - 5/7 + 5/21 × 9/25
= - 5/7 + 45/525
= - 5 x 75 / 7 x 75 + 45/525
= - 375/525 + 45/525
= - 330/525
= 15 x - 22 / 15 x 35
= - 22/35

B) 25/17 ÷ 15/4 - 11/3
= 25/17 x 4/15 - 11/3
= 100/255 - 11/3
= 100/255 - 11 x 85 / 3 x 85
= 100/255 - 935/255
= - 835/255
= 5 x - 167 / 5 x 51
= - 167/51

C) 5/4 - 2/5 × 10/3
= 5/4 - 20/15
= 5 x 15 / 4 x 15 - 20 x 4 / 15 x 4
= 75/60 - 80/60
= - 5/60
= 5 x - 1 / 5 x 12
= - 1/12