Mr. Lu owns a computer store. For last month, half of their sales are laptops, one-third are netbooks, and the rest are desktop computers. If Mr. Lu's store was able to sell a total of 72 computers, how many of them are desktop computers? Think carefully first, then make a decision:
There were 72 / 2 = 36 laptops sold. There were 72 / 3 = 24 netbooks sold. So, there were a total of 36 + 24 = 60 laptops and netbooks sold. Thus, 72 - 60 = 12 desktop computers were sold last month. So, the answer is 12.