Bonjour,

Diviser par un nombre, c'est multiplier par son inverse

a) 42 ÷ 3,5

= 42 ÷ 7/2

= 42 × 2/7

= (42 × 2)/7

= (6 × 7 × 2)/7

= 6 × 2

= 12

b) 140,3 ÷ 0,8

= 1403/10 ÷ 8/10

= 1403/10 ÷ 4/5

= 1403/10 × 5/4

= (1403 × 5)/(10 × 4)

= (1403 × 5)/(5 × 2 × 4)

= 1403/(2 × 4)

= 1403/8

c) 0,652 ÷ 2,5

= 652/1000 ÷ 5/2

= 326/500 ÷ 5/2

= 163/250 ÷ 5/2

= 163/250 × 2/5

= (163 × 2)/(250 × 5)

= (163 × 2)/(125 × 2 × 5)

= 163/(125 × 5)

= 163/625

d) 99 ÷ 0,6

= 99 ÷ 6/10

= 99 ÷ 3/5

= 99 × 5/3

= (99 × 5)/3

= (33 × 3 × 5)/3

= 33 × 5

= 165