Its wrong. the descending order should be :
ahmad
ali
akbar
nasir
shehbaz

Solution:

ahmad > 3*ali
ali > 5*akbar
akbar > 0.5*nasir
nasir> 0.5*shehbaz

1) heaviest is Ahmad
2) lightest is shehbaz
3) shehbaz is lighter than all students
4) shehbaz is heavier than no one.
5) Descending order :
ahmad
ali
akbar
nasir
shehbaz