Question

The average weight of $A,B,C$ is $45kg$ . If the average weight of $A$ and $B$ be $40kg$ and that of $B$ and $C$ be $43kg$, find the weight of $B$ ?

• A. $21kg$
• B. $20kg$
• C. $38kg$
• D. $31kg$

Answer 1

Answer: (D)

$31kg$

$\frac{A+B+C}{3}=45$ $kg$

$\Rightarrow A+B+C=45\times 3=135$ $kg$

$\Rightarrow \frac{A+B}{2}=40$ $kg$

$\Rightarrow A+B=80$ $kg$

$\therefore C=135-80=55$ $kg$

$\Rightarrow \frac{B+C}{2}=43$ $kg$

$\Rightarrow B+C=86$ $kg$

$\therefore B=86-55=31$ $kg$

$\therefore$ The weight of $B$ is $31$ $kg$.