In video number 44 from The Little BIG Things Video Series, Tom does the math for you. It all comes down to lunch. Never Waste a Lunch!
You can find the video in the right column of the front page of tompeters.com or you can watch the video on YouTube. [Time: 2 minutes, 18 seconds] You can also download a PDF transcript of the video's content: Strategy: 12 x 20 = 240.