How to solve : a store sells two kinds of candles, scented and unscented. the scented candles burn 1/12 inches in 20 minutes. then unscented candles burn 1/6 inches in 30 minutes. which type of candle burns in 1 hour and what is its burn rate?

The first thing we must observe is that the hourly rate for each candle is:

 scented candles:
 (1/12) / (20/60)
 Simplifying:
 = (1/12) / (10/30)
 = (1/12) / (5/15)
 = (1/12) / (1/3)
 = (3/12)
 = (1/4) inches / hour

 Unscented candles:
 (1/6) / (30/60)
 Simplifying:
 = (1/6) / (15/30)
 = (1/6) / (3/6)
 = (1/6) / (1/2)
 = (2/6)
 = (1/3) inches / hour

 
 The unscented candles burn faster at a rate of:
 (1/3) inches / hour