5000 lei ... 100%
600 lei ... d % (d= dobanda/an)
--------------------------
d = (600*100) : 5000 = 60000 : 5000 = 60:5=12 %
sau
5000 lei ... 100%
5600 lei ... x %
--------------------------
x = 100*5600 : 5000 = 560000 : 5000 = 560:5=112%
=> d =112% - 100% = 12%