A mathematician, an engineer and a physicist sat around a table discussing how to measure the volume of a cow.

The mathematician suggested the use of geometry and symmetry relationships of the cow, but his idea was rejected on the grounds of being too time consuming.

The engineer suggested placing the cow in a pool of water and measuring the change in the height of the water, but his idea was rejected on the grounds of impracticality.

"It's easy," said the physicist. "We'll make an asumption that the cow is a small sphere, calculate the volume and then blow it up to the actual size."