we have, index size =40B(CK)+10B(POINTER)=50 B
blocking factor = 1000/50=20records/block
Number of first level index records =20,000
Number of first level blocks =20000/20=1000blocks
number of second level blocks 1000/20=50blocks
number of third level blocks = 50/20=3blocks
number of fourth level blocks =3/20=1block
so total levels will be 4