A dishonest trader using a faulty balance makes a profit of 5% while buying as well as while selling his goods. His actual gain percent in the whole process amounts to,
10.25%
Let the actual cost of goods be ₹ 100.
While buying the trader makes a 5% profit. That means he buys ₹ 105 worth of goods by paying ₹ 100.
While selling he makes again a profit of 5% on ₹ 105
Applying the second profit of 5% on ₹ 105, we get SP =₹105(1+0.05)=₹105×1.05=₹110.25
So the net profit is,
110.25 − 100 = ₹ 10.25.
Profit%=profitCost price×100
Profit%=10.25100×100
=10.25%
So, the gain per cent in the whole process amounts to 10.25%