Help! Urgent! Normal distribution

Ques:

Price of a pair of shoes has normally distributed with mean RM126.50 and standard deviation RM11.80.

(a) A man wants to buy 4 pairs of shoes randomly. Find probability:

i) Total price of shoes which is between Rm460 and Rm520.

ii) Average price of shoes which is between Rm115 and Rm130.

(b) A man wants to buy 25 pairs of shoes randomly. Fond probability that average price less than RM 128.

(c) If the man buy 100 pairs of shoes randomly, find the probability that average price less than RM128.

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Re: Help! Urgent! Normal distribution

Re: Help! Urgent! Normal distribution

Erm... for a) I use this formulae. P[(460-(4xmean))/16xstardard deviation)

Others no idea... I don't know the formulae used is correct or not for other ques. Thanks for concern.