At the interbank foreign exchange market, the rupee weakened sharply by 100 paise, to 64.20 per dollar in late morning trade, today, on good demand for the US currency from banks and importers, amid a rise in crude oil prices. The rupee had closed at 63.20 against the dollar, last Friday.In the global market, the US dollar swung between small gains and losses against major currencies, after US Federal Reserve, or central bank officials wrapped up a yearly gathering, appearing ready to start slowing monetary stimulus next month.