Today, while buying Nanfu (南孚) No. 6 batteries, I discovered a small trick.

There were two versions on the shelf:

One was a rectangular pack with 8 batteries for 19.9 yuan; the other was a square pack with 6 batteries plus 1 free (buy 6 get 1), actually 7 batteries, for 14.5 yuan.

If you don't calculate carefully, you might easily grab the 8-battery pack because it looks obviously "more." But when you actually count, it's only one more battery.

Let's calculate the unit price: The 8-battery pack is about 2.49 yuan per battery; the 7-battery pack is about 2.07 yuan per battery.

In other words, each battery in the 8-battery pack is actually over 0.4 yuan more expensive.