A machine is adjusted such that the average weight of the detergent boxes is 500g.

The weight distribution of the boxes is normal with s = 25g.

Due to the many vibrations undergone by the machine it is believed that the average filling weight would be reduced.

Samples from 60 containers are taken at random on a regular basis to verify the correctness of the machine fit.

The average weight of the detergent boxes would be less than 500g if the average weight of the sample is less than 494.69g

Calculate the power of the test if in fact the true population mean is 492.