Bob took John's $ 100 and went to the store.
On the way, John lost his money.
Bob took Jim from $ 50 and went on to the store.
In the store, Bob bought two chocolates for $ 10 for $ 20.
After the purchase, Bob had $ 30 left, which he returned to John (he must have left $ 70).
As a result, he remained due to John $ 70 and Jim $ 50 (only $ 120).
He also has an asset - two chocolates for $ 10 (only $ 20).
Must 120 $ + asset 20 $ = only 140 $.
Question: where did $ 10 go missing?
What do you think ?