4 . An investigation was carried out into the number of seconds that cargo trains are late in departing . A random sample of n cargo trains is observed . Let X be the number of seconds that a cargo train is late in departing . It is given that X � 16.6 ,
2 sn � 1
� 3.3 .
( a ) Write down an unbiased estimate of
( i ) the population mean ; s � 3.27 and
2 n
( ii ) the population variance .
( b ) Find n .
[ 2 ]
[ 3 ]
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