4 . The weight w of a bronze container , in kilograms , produced in a factory is studied . A random sample of n containers was weighed . It is given that w � 70 kg , s � 1
� 3 kg and
2 16 2 s � n�1 sn
15 .
( a ) Find n . [ 3 ]
( b ) Construct a 90 % confidence interval for the population mean , giving the answer to three decimal places .
[ 2 ] ( c ) Hence , write down the interval width of the confidence interval , giving the answer to two decimal places . [ 1 ] n
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