Question

You saw a shirt for $97. You didn’t have the cash, so you borrowed $50 from your mum and $50 from your dad = $100. You bought the shirt, and had $3 change. You gave your dad $1 and your mum $1 and kept the other $1 for yourself. Now you owe your mum $49 and your dad $49. 49+49 = 98 + your $1 = 99. Where is the missing $1?

Answer 1

The $1 isn't missing, the last equation just doesn't make sense
If you're adding what you owe and what you have, you need to make one or the other negative. It just doesn't make sense for them to both to be positive.