A sweet girl is willing to help even a stranger
One afternoon, Brenda had her lunch alone at a restaurant. But unfortunately, when she was eating halfway, she noticed a young man in tears. Worried that something was probably amiss, she asked what was wrong. She found out from the man's girlfriend and mother (who were also present) that the man ate something too spicy (probably trying to impress his girlfriend).
Being the sweet and sensitive girl, Brenda interrupted her meal, offered the man some tissue to wipe his tears and bought him a drink to alleviate the spicy feeling. The young man, his girlfriend and mother were so touched by Brenda's kindness and good-naturedness that they each gave her $10 (totalling $30). But a few minutes later, she felt only $25 was enough so she decided to give them back $5. But she could not divide $5 evenly among the three of them so she kept $2 for herself and gave the man, his girlfriend and mother $1 each.
Now the young man, his girlfriend and mother each gave Brenda $10 but received $1 each at the end which means each of them gave Brenda $9. This gives us a total of $27. Brenda kept $2 for herself. So $27 + $2 = $29. But the young man, his girlfriend and mother gave Brenda $30 in total initially.
Who had the missing dollar?