A massive fall in petrol prices has pushed the cost of living down for the first time in two years and opened the way for interest rates to fall to as low as 2.5 percent.Petrol prices fell by more than 18 percent in the December quarter as unleaded petrol fell from around $1.50 per litre in September to close to $1.00 per litre in December, mirroring falling oil prices.According to official figures released today, the consumer price index – which tracks the cost of living in Australia – fell by 0.3 percent in the December quarter. Over the 12 months to December, the CPI rose by 3.7 percent, well below its previous reading of 5 percent.The fall in the cost of living - which is the fastest decline logged in 10 years - is expected to open the way for further rate cuts from the Reserve Bank of Australia (RBA), starting with its first meeting of the year, to be held next week.Economists expect the RBA to trim the cash rate by 75 basis points, a move that would take the cash rate to 3.5 percent.“There’s nothing of concern in these figures for the Reserve Bank that will stop it aggressively cutting interest rates next week,” Riki Polygenis, economist at ANZ Bank told ninemsn.She believes rates will fall by 75 basis points next week and will ventually fall to 2.5 percent this year.While the fall in prices and interest rates may be good news for consumers, other economic figures released today showed a sharp slowdown in economic activity.The Westpac/Melbourne Institute index of economic activity - which tracks the likely pace of economic growth in the future - contracted by 2.2 percent in November, and analysts said it showed that the odds of Australia entering a recession this year are shortening.“With the –2.2 percent growth rate for November we are now reporting the first negative reads for growth since May 2001,” said Bill Evans, Westpac’s chief economist. “In the past this has been a useful signal ofthe likelihood of Australia experiencing a recession.