Listing is for finite or "countable" sets -whatever that means to you.
49. list x-value(s) for which the equality holds
50. 0,1,2,3,4 since 5!=120
51. 0,1,2,3,4,5,6,7
52.a. P (10,3) order matters
b. P (6,3)
c. could be answer to a but I am not entirely sure.
Follow for solutions.
Grapefruit=108
Orange=100
Apple=90
a) (108-90)/90*100 = 18/90*100=20%
b) (108-90)/108= 18/108*100=16 2/3%