(a) A consumer organisation is testing two different brands of battery. A sample of 15 of brand A shows an average useful life of 410 hours with a standard deviation of 20 hours. For brand B, a sample of 20 gave an average useful life of 391 hours with standard deviation 26 hours. Test whether there is any significant difference in battery life.

(b) What assumptions are being made about the populations in carrying out this test?