Find the mean of the data set. if necessary, round to the nearest tenth 18.1, 17.9, 16.8, 18.7, 15.1

Ineed i been stuck on this question since yesterday

Aword processing program requires a 7- digit registration code made up of the digits 1,2,4,5,6,7 and 9 each number has to be used and no number can be used mor than once how many codes are possible

Jonathan can type 20 documents in 40 minutes ,and susan can type it in 30 minutes and jack can type it in 24 minutes working together ,how much time will it is take them type the same document