The spending (HK$) of a sample 10 customers in a restaurant is recorded in an ordered array as below: 55, 58, 63, 66, 72, 75, k, 80, 88, 90
(a) It is known that the sample mean spending of the above data is HK$ 72.5, find the value of k.
(b) Find the sample standard deviation of the above data.
(c) Find the third quartile of the above data.
(d) During the Lunar New Year holiday, there is a 30% marked up on the prices and an additional fixed service charge of $15 is applied. Find the sample mean and sample standard deviation of the spending of a customer during the Lunar New Year holiday
part a b c were answer ,only d is unknown