Page 230 - DMTH404_STATISTICS

Statistics

Notes Assuming a cut-off scores of 70, (i) what percentage of the experienced group is likely to be
rejected, (ii) what percentage of the fresh group is likely to be selected, (iii) what will be
the likely percentage of fresh candidates in the selected group? Assume that the scores are
normally distributed.
Hint : See example 33.

11. 1,000 light bulbs with mean life of 120 days are installed in a new factory. Their length of
life is normally distributed with standard deviation of 20 days. (i) How many bulbs will
expire in less than 90 days? (ii) If it is decided to replace all the bulbs together, what
interval should be allowed between replacements if not more than 10 percent bulbs should
expire before replacement?
Hint : (ii) P(X £ X ) = 0.9.
1
Answers: Self Assessment

1. (a) 2. (c) 3. (b) 4. (d) 5. (a)

15.8 Further Readings

Books Introductory Probability and Statistical Applications by P.L. Meyer
Introduction to Mathematical Statistics by Hogg and Craig

Fundamentals of Mathematical Statistics by S.C. Gupta and V.K. Kapoor

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