ex.4)
terrain 3.5 ha dont 4/5 occupés par des arbres fruitiers soit 3.5 ha x 4/5 = 2.8 ha occupés par des arbres fruitiers
dont 2/7 de pommiers, soit 2.8 ha x 2/7 = 0.8 ha de pommiers = 8000m²
ex.5)
a/ 1/10 + (1/2 x 2/5) = 1/10 + [(1x2)/(2x5)] = 1/10 + 2/10 = 3/10
b/ 1/3 x (2/5 +3/10) = 1/3 x [(2x2)/(5x2) + 3/10] = 1/3 x 4/10 +3/10 = 1/3 x 7/10 = (1x7)/(3x10) = 7/30
c/ 41/12 - [5/2 x (2/3 +5/6)] = 41/12 -[5/2 x (4/6 + 5/6)] = 41/12 - [5/2 x 9/6] = 41/12 - 45/12 = (41-45)/12 = -4/12 = (-1x4)/(3x4) = -1/3
