Data:
1. Ahmad weighs thrice as much as Ali
Ahmed=3(Ali)

2. Ali weighs five times as much as Akbar
Ali=5(Akbar)

3. Akbar weighs half as much as Nasir
Akbar=1/2(Nasir)

4. Nasir weighs half as much as Shehbaz
Nasir=1/2(Shahbaz)

Solution:

Ahmed=3(Ali)
Ali=5(Akbar)
Akbar=1/2(Nasir)
Nasir=1/2(Shahbaz)

Let
Ahmed=a
Ali=b
Akbar=c
Nasir=d
Shahbaz=e

So,
a = 3b
b = 5c
c = 1/2(d) = 0.5d
d = 1/2(e) = 0.5e

Or,
a=3b
b=5c
d=2c
e=2d

As,
a=3b
and
b=5c

So,
a=3(b)=3(5c)=15c
a=15c

Similarly,
e=2d
and
d=2c

So,
e=2(d)=2(2c)=4c
e=4c

Now,
a=15c
b=5c
d=2c
e=4c

Arranging in descending order

a=15c
b=5c
e=4c
d=2c
c=c

In other words
Ahmed = 15(Akbar)
Ali = 5(Akbar)
Shahbaz = 4(Akbar)
Nasir = 2(Akbar)
Akbar = Akbar

So,
i. Who is the heaviest in weight?
Ahmed

ii. Who is the lightest in weight?
Akbar

iii. Shahbez is lighter in weight than which of the two students?
Ahmed and Ali

iv. Shahbez is heavier in weight than which of the two students?
Nasir and Akbar

v. Show the descending order of weights of the two students?
1. Ahmed
2. Ali
3. Shahbaz
4. Nasir
5. Akbar