NOTE :- When a person sell two similar items , one at the loss of say x% and another at the gain of x% , then the seller always incurs the loss given by
Loss % = (Common Loss and gain %/10)² = (x/10)²
Hence , the answer of the above question is :
Common gain and loss % = 25
Loss % = (25/10)² = 25*25 /10*10 = 625/100 = 6.25
Hope this helps You!!