Bonjour
A=(1/4-1/5):(1/2+1/3)
A = [(1 x 5) / (4 x 5) - (1 x 4) / (5 x 4)] : [(1 x 3) / (2 x 3) + (1 x 2) / (3 x 2)]
A = (5/20 - 4/20) : (3/6 + 2/6)
A = 1/20 : 5/6
A = 1/20 x 6/5
A = 6/100
A = (2 x 3) / (2 x 50)
A = 3/50.