I had some of my books which were now no use to me, so I wanted to sell them.
I sold half of them at 40% loss then half of the remaining at 40% gain and the remaining at same price as the selling price.
What was net profit % or loss%.
For simplicity, let us suppose that you have 100 books that you sell for $1 each
Total value of your expected sales = $100
Selling (1/2) of these at a 40% loss ....you realize .60 *50 = $30
Selling 1/2 of the remaining books at a 40% gain you realize (25) * 1.40 = $35
Selling the remaining books you realize 25 * 1 = $25
So....the amount you make = $ [30 + 35 + 25 ] = $90
So you absorb a loss of (100 - 90] / 100 * 100% = (10/100) * 100% = 100%/10 = 10%