Farah thinks that when she deposits her money in a bank, the bank locks her exact money away in a…

Why

Farah's guess is a natural extension of what she knows from her own piggy bank — money goes in, the same money presumably sits there waiting, and comes out again untouched. A bank actually works quite differently from a piggy bank, and that difference is exactly its purpose. When Farah deposits money, the bank doesn't lock her particular notes away; it records that she is owed that amount, and then lends much of that same pool of money out to other people — for a shop's new equipment, a family's home, a farmer's seeds — who pay the bank back with a little extra, called interest, over time. That's also why banks can afford to pay Farah interest on her own deposit: her money isn't sitting idle, it's out working, earning more money, of which she gets a small share back. Test: ask why a bank pays you interest for keeping money there, while a piggy bank pays nothing at all — the bank is doing something active with the money in between, which is exactly the source of that extra payment. No, the bank also puts deposited money to use: it lends deposits onward rather than storing them untouched, and that lending is the very reason banks can pay interest at all.