First we have to find how many books he sold, so
75+50+64+68+163=420 - total books sold
Now im finding how many books are not sold
1200-420=780
Now we can use proportion, so
1200 ---------100%
780------------x
x=\(x= \frac{780*100}{1200}=65%\) 65% of all books are not sold.