I borrowed $50 from mum and $50 from dad to buy a bag costing $97. After the purchase, I had $3 left. I returned $1 to dad and $1 to mum, and reserved $1 for myself. I now owe $49+$49=$98 plus the $1 I reserved for myself, which is $99. Where is the missing $1?
Why is [math] - 1 \times - 1 = 1 [/math]?