9 . In a supermarket , the weights of apples are normally distributed with mean 140 g and standard deviation 9 g , and the weights of oranges are normally distributed with mean 200 g and standard deviation 14 g . Three apples are randomly chosen . Let X be the total weight of the selected apples .
( a ) Write down
( i ) the mean of X ;
( ii ) the variance of X .
Three apples and seven oranges are randomly chosen . Let Y be the total weight of the selected fruits .
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( b ) Write down
( i ) the mean of Y ;
( ii ) the standard deviation of Y .
( c ) Hence , find P ( Y � 1770 ) .
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