Page 440 - DMTH404_STATISTICS

Statistics

Notes 5. Samples of two types of electric bulbs were tested for length of life (in hours) and the
following data were obtained :

Type I Type II

Sample size 9 8

Mean of the sample 1235 1125

.
.

S D of the sample 30 35
Test, at 5% level of significance, whether the difference in sample means is significant?
Hint : Use small sample test, i.e., t-test.
6. A company selects 9 salesmen at random and their sales figures for the previous month
are recorded. These salesmen then undergo a course devised by a business consultant and
their sales figures for the following month are compared as shown in the following table.
Has the training course caused an improvement in the salesmen's ability? Let the level of
significance be 5%.
Previous Month 75 90 94 85 100 90 69 70 64
Following Month 77 101 93 92 105 88 73 76 68

Hint : Use paired t-test to test H :  ³  against H :  <  .
0 1 2 a 1 2
7. A trader wants to compare the delivery times for two suppliers A and B. The trader wishes
to continue with his current supplier A if his mean delivery time is less than or equal to
that of supplier B, otherwise will switch over to B. He has obtained the following two
independent samples for the above purpose :
Supplier A : n = 40, X = 10 days , S = 3 days
1 1 1

Supplier B : n = 30, X = 8 days , S = 4 days.
2 2 2
Answers: Self Assessment

1. (i) precision (ii) one (iii) standard (iv) pooled (v) small (vi) F (vii) one (viii) s = s
1 2
(ix) significant (x) small.

31.9 Further Readings

Books Sheldon M. Ross, Introduction to Probability Models, Ninth Edition, Elsevier
Inc., 2007.

Jan Pukite, Paul Pukite, Modeling for Reliability Analysis, IEEE Press on
Engineering of Complex Computing Systems, 1998.

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