The Luminous Fish Effect - S1-E4
Corrected entry: When Penny and Sheldon are driving to the supermarket, Sheldon is explaining the weight of the car and how it affects her braking time. He estimates the car's weight to be 4000 pounds, 140 for himself and 120 for Penny, and then rounds the total up to be 4400 pounds, when it actually should be 4260. It's extremely out of character for somebody like Sheldon to make such a basic addition mistake.
Correction: Or he could be including other things he just failed to mention, such as the contents of the vehicle and trunk.
LorgSkyegon