Explanation:

- The total weight of 15 students is 15 * 40 kg = 600 kg.

- When one student leaves, there are 14 students left.

- The new total weight of 14 students is 14 * 39.5 kg = 553 kg.

- The weight of the student who left is 600 kg - 553 kg = 47 kg.

Answer: Option 1, 47 kg

- Option 1: 47 kg — This option matches the calculation.

- Option 2: 42 kg — This is incorrect based on the calculation.

- Option 3: 52 kg — This is incorrect based on the calculation.

- Option 4: 48 kg — This is incorrect based on the calculation.