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4.Average
hard
The average weight of $A , B$ and $C$ is $45\, kg$. If the average weight of $A$ and $B$ is $40 \,kg$ and that of $B$ and $C$ is $43\, kg$, then the weight of $B$ is
A
$17$
B
$20$
C
$26$
D
$31$
Solution
Weight of $A+B+C=45 \times 3=135 kg$…..$(1)$
Weight of $A+B=40 \times 2=80 kg$…..$(2)$
Weight of $B + C =43 \times 2=86 kg$…..$(3)$
Subtracting (2) from (1),
Weight of $C=135-80=55 kg$…..$(4)$
Subtracting (3) from (1),
Weight of $A=135-86=49$ kg…..$(5)$
Subtracting (5) from (2),
Weight of $B=80-49=31 kg$…..$(6)$
Standard 13
Quantitative Aptitude