The average weight of A, B, C is 40 kg, the average weight of B, D, E is 42 kg and the weight of F is equal to that of B. What is the average weight of A, B, C, D, E and F?

Here's a brief explanation:

1. Sum of weights of A, B, C: Since their average is 40 kg, their total weight is 3 * 40 kg = 120 kg. (Equation 1)
2. Sum of weights of B, D, E: Since their average is 42 kg, their total weight is 3 * 42 kg = 126 kg. (Equation 2)
3. We are given that the weight of F is equal to the weight of B (F = B).
4. We need to find the average weight of A, B, C, D, E, and F. This means we need the total weight (A + B + C + D + E + F) divided by 6.
5. Substitute F with B in the total sum: (A + B + C + D + E + B) = (A + 2B + C + D + E).
6. Now, add Equation 1 and Equation 2: (A + B + C) + (B + D + E) = 120 kg + 126 kg A + 2B + C + D + E = 246 kg
7. This sum (246 kg) is exactly the total weight of A, B, C, D, E, and F (since F=B).
8. Average weight = Total weight / Number of people = 246 kg / 6 = 41 kg.

Therefore, the average weight of A, B, C, D, E and F is 41 kg.

Analyzing the options: A) 40.5 kg - Incorrect. B) 40.8 kg - Incorrect. C) 41 kg - Correct, as calculated above. D) Cannot be determined as data is inadequate - Incorrect, as we were able to determine the average.