So, we do secret Santa for the adults. There's a €100 limit on the spend, and my brother has told me what he wants. First part of the present is sorted, €30, the second part is €70 so bang on. But, the shop where I got the second part (a sports store) was having a special offer, buy one get one half price. I need new runners, the ones I wanted were also in the offer, so I got them. I've just realised that my brother's item was the cheaper one, so it was actually half price. Do I have to go buy him something else for €35, or can I claim that as "my" saving on my runners?? Or do I split the difference?