Step-by-Step Weight Ranking

To find the lightest person, we can establish the weight order of the five individuals (K, L, M, P, Q) by placing them in five ranked slots from heaviest to lightest.

Ranking: 1st (Heaviest) > 2nd > 3rd > 4th > 5th (Lightest)

1. Applying the Clues

Clue: "L is the heaviest."

• This places L in the 1st position: L > __ > __ > __ > __

Clue: "the number of people heavier than P is the same as the number of people lighter than Q."

• Let's test the possibilities for P's rank (he cannot be 1st, as L is heaviest):
  
  • If P is 2nd (1 person heavier), then Q must be 4th (1 person lighter). This is a valid scenario.
  • If P is 3rd (2 people heavier), then Q must be 3rd (2 people lighter). This is impossible as they have different weights.
  • If P is 4th (3 people heavier), then Q must be 2nd (3 people lighter). This is also a valid scenario.
• This leaves us with two possible scenarios.

Clue: "K is not the lightest."

• This means K cannot be in the 5th position.

2. Analyzing the Scenarios

Let's determine the lightest person in each of the two possible scenarios.

Scenario 1: P is 2nd and Q is 4th.

• The ranking is: L > P > __ > Q > __
• The remaining people to be placed in the 3rd and 5th spots are K and M.
• Since K cannot be the lightest (5th), K must be in the 3rd spot.
• This leaves M to be in the 5th spot, making M the lightest.

Scenario 2: Q is 2nd and P is 4th.

• The ranking is: L > Q > __ > P > __
• The remaining people to be placed in the 3rd and 5th spots are K and M.
• Again, since K cannot be the lightest (5th), K must be in the 3rd spot.
• This leaves M to be in the 5th spot, making M the lightest.

Conclusion

In both logically possible scenarios, the person in the lightest position is M. Therefore, M is the lightest.