How Many Jobs Do We Need: Teaching Arithmetic To Economists

I hate to harp on a seemingly small point, but it does offend me that professional economists and people who write on economics have such an aversion to simple arithmetic. One of the numbers that frequently in appears in discussions on the state of the economy is the number of jobs that we need to keep pace with the growth of the labor force. I have consistently been using 90,000 a month, however I see considerably higher numbers routinely thrown out, sometimes as high as 150,000 a month...