This is a beauty !!..
well,
ST-1
The total number of books sold on Thursday -- 8
That means it should be that number of books sold on friday would be more than 8, but it can be 10,11,12....so on...
So ST-1 is insufficient and divulges nothing.
ST-2
The total no.of books sold on saturday --> 38.
Remaining 52 books would be sold on the previous 5 days.
let us imagine that at max, 10 books are sold on each day from Monday to friday => 5x10 = 50 books ...
But it was said that Friday has the second highest sale , so the no.of books sold on friday would be greater than books sold on any other day.
How about remaining 2 books , these two books has to be on friday i,e total of 12 books are to be sold on friday.
OR
11 books cannot be sold on friday.(more than 11 has to sold to make friday second highest sales day)
Hope this helps.
So ST-2 is sufficient.
Nice post.
Thanks
Keep rocking !