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The CEO then told him that some of the floors could not handle more than 500 pounds of pressure, so rolling a 2,000-pound server would cause damage. Musk replied that the servers had four wheels, so the pressure at any one point was only 500 pounds. “The dude is not very good at math,” Musk told the musketeers.

Musk not very good at understanding that even if his arithmetic was accurate (article states earlier that the weight was higher), that's only true if the racks are perfectly balanced and not moving.