The mean life of a sample of 10 electric light bulbs was

found to be 1456 hours with standard deviation of 423

hours. A second sample of 17 bulbs chosen from a

different batch showed a mean life of 1280 hours with

standards deviation of 3988 hours. Is there a significant

difference between the means of the two batches. Take 5

per cent level of significance. (Given calculated value of

t-statistics at .05 level of significance is 2.06).