6. Data set A: n = 9, x = 72, s = 5 I Data set B: n = 16, x, = 1042,* s2=17 - x; Data set C: n = 5, x3 = 70, x = 24680 (a) The three sets are mixed. Find the mean and standard deviation for the 30 numbers. (b) It was later found that in each set, a wrong entry had been made, as follows: Set A B C True datum 69.5 63.8 Unknown Wrong entry 65.9 68.3 72.5 Frequency 2 3 1 Find the true mean and standard deviation for the 29 correct data, having excluded the entry "72.5" from C.