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?

The correct option is 41 kg.

Let the weights of A, B, C, D, E, and F be represented by $A$, $B$, $C$, $D$, $E$, and $F$ respectively.

From the first statement, the average weight of A, B, and C is 40 kg:
$\frac{A+B+C}{3}=40$
Multiplying both sides by 3, we get the sum of their weights:
$A+B+C=120\text{kg}$ (Equation 1)

From the second statement, the average weight of B, D, and E is 42 kg:
$\frac{B+D+E}{3}=42$
Multiplying both sides by 3, we get the sum of their weights:
$B+D+E=126\text{kg}$ (Equation 2)

We are also given that the weight of F is equal to the weight of B:
$F=B$ (Equation 3)

We need to find the average weight of all six individuals (A, B, C, D, E, and F):
$\text{Average Weight}=\frac{A+B+C+D+E+F}{6}$

Let's find the total sum of their weights, $A+B+C+D+E+F$, by substituting Equation 3 ($F=B$) into the sum:
$\mathrm{Sum}=(A+B+C)+(D+E+B)$

Notice that we can rewrite this sum using Equation 1 and Equation 2:
$\mathrm{Sum}=(A+B+C)+(B+D+E)$
Substituting the values from Equation 1 and Equation 2:
$\mathrm{Sum}=120+126=246\text{kg}$

Now, we calculate the average weight by dividing the total sum by the number of people, which is 6:
$\text{Average Weight}=\frac{246}{6}=41\text{kg}$