Solutions
Seven friends: B, Q, X, Y, T, Z and V
1) T is heavier than X and Z.
T > X/Z
2) T is lighter than V but heavier than B.
V > T > B
3) X is heavier than Y but shorter than V.
V > X > Y
4) Q is lighter than Z.
Z > Q
5) Z is lighter than B.
B > Z
6) After combining (4) and (5)
B > Z > Q
7) After combining (2) and (6)
V > T > B > Z > Q
8) X is the third lightest person.
1 > 2 > 3 > 4 > X > 6 > 7
9) Q is not the lightest person.
V > T > B > Z > X > Q > Y
48kg 21kg
Clearly, Z is just heavier than X is the only true statement among the given statements with respect to the given arrangement.