A long time ago, a coworker bought a surplus water tank and was curious how much it would weigh when filled. I asked him the dimensions, and as he was talking I

A long time ago, a coworker bought a surplus water tank and was curious how much it would weigh when filled. I asked him the dimensions, and as he was talking I converted everything to inches, multiplied by 2.5 to get approximate cm, rounded to the nearest power of 2 and added the exponents, and used 3 as the value of pi (it was a cylinder). Using 1 cm³ of water = 1 gram, I divided by 1000 (or was it 1024?) to get the weight in kg, and finally multiplied by 2.2. I was able to give him an answer by the time he was done.