This is not true. The average daily interest rates on lending BTC or any other coin vary significantly, and offer much lower interest. Poloniex deducts its own 0.15/0.25% fee on every coin-coin (fiat-coin) exchange. Have you doubled your coins? No? You're simply misleading others. If somebody's lucky enough they'll earn around 10% yearly at the very best
RE: How to multiply your Bitcoins the old school way