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
