a) x/4 = 3/5
x = (4*3)/5 = 12/5
b) 10/x = 1/4
x = (10*4)/1 = 40
c) 4/9 = x/2
x = (4*2)/9 = 8/9
d) 3/8 = 9/x
x = (9*8)/3 = 3*8 = 24
e) x/(1/3) = (7/10) / (3/10)
x/(1/4) = (7/10) * (10/1) = 7/1 = 7
x = 7*(1/4) = 7/4
f) 0,4/x = 0,05/0,3
x = (0,4 * 0,3) / 0,05 = 0,12/0,05 = 12/5
g) x/0,5 = 0,7/0,35
x = (0,5 * 0,7)/0,35 = 0,35/0, 35 = 1
h) (1/2 + 1/5) / x = 7/10
x = [(1/2 + 1/5) * 10] / 7 = [(5/10 + 2/10) * 10]/7 = [{7/10) * 10]/7 = 7/7 = 1
i) x/16 = (0,75 + 1/4)/8
x = [16 * (3/4 + 1/4)]/8 = (16 * 4/4)/8 = 16/8 = 2
j) [1/4 + (1/4):4]/15 = x/4
x = 4*[1/4 + (1/4)*(1.4)]/15 = 4*(1/4+1/16)/15 = 4*(4/16 + 1/16)/15 = 4*(5/16)/15 = (5/4)/15 = (5/4)*(1/15) = 1/12
cele cu perioade nu le stapanesc bine, dar celelalte sunt sigur corecte
