[Studio25]

It depends on the base of your calculation. With your example, it depends whether you use the £10 cost price or the £110 sale price as your starting point. The way you and I work it out, it's a 1,000% profit, because the sale price of eleven times the cost price means a profit margin ten times the cost price.

With Bobs base of the selling price for profit calculation, the base price is 9% of the cost price meaning the profit is 91%

There is no "right" or "wrong" answer, but it does illustrate the need to understand how any given statistic is calculated.