Explanation:

Let's break down the problem:

- Let the number of boys be B and girls be G.

- Total students = 100, so: B + G = 100.

- Total weight = 100 × 46 = 4600 kg.

- Weight of boys = B × 50 kg.

- Weight of girls = G × 40 kg.

- So, B × 50 + G × 40 = 4600.

Solving equations:

1. B + G = 100

2. 50B + 40G = 4600

From (1): G = 100 - B

Substitute into (2):

50B + 40(100 - B) = 4600

50B + 4000 - 40B = 4600

10B = 600

B = 60, G = 40

Difference = |60 - 40| = 20

Options:

- Option 1: 30 (Not correct)

- Option 2: 25 (Not correct)

- Option 3: 20 (Correct)

- Option 4: 10 (Not correct)

Option 3: 20 is the correct answer.