Réponse :
Bonjour
Explications étape par étape :
A = 1/2-1/2÷5/4
A = 1/2 - 1/2 * 4/5
A = 1/2 - (1*2*2/2*5)
A = 1/2 - 2/5
A =((1*5)/(2*5))/((2*2)/(5*2))
A = 5/10 - 4/10
A = 1/10
B = (3/4+2/5)×1/23
B = ((3*5)/(4*5)/(2*4)/(5*4)) * 1/23
B = (15/20)+(8/20)) * 1/23
B = 23/20 * 1/23
B = (23*1)/(20*23)
B = 1/20