Average age of A, B and C is 84 text{ years}. | vedclass

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(A) The average age of $A, B$ and $C$ is $84 	ext{ years}$,so $A + B + C = 84 	imes 3 = 252$ ......$(1)$When $D$ joins,the average age of $A, B, C$

Vedclass · Accepted Answer

$80$

Vedclass · Answer

(A) The average age of $A, B$ and $C$ is $84 	ext{ years}$,so $A + B + C = 84 	imes 3 = 252$ ......$(1)$When $D$ joins,the average age of $A, B, C$ and $D$ becomes $80 	ext{ years}$,so $A + B + C + D = 80 	imes 4 = 320$ ......$(2)$Subtracting $(1)$ from $(2)$,we get $D = 320 - 252 = 68 	ext{ years}$.Given that $E$ is $4 	ext{ years}$ older than $D$,so $E = 68 + 4 = 72 	ext{ years}$.When $E$ replaces $A$,the new average of $B, C, D$ and $E$ is $78 	ext{ years}$,so $B + C + D + E = 78 	imes 4 = 312$.Substituting the values of $D$ and $E$,we get $B + C + 68 + 72 = 312$,which simplifies to $B + C + 140 = 312$,so $B + C = 172$ ......$(3)$Finally,substituting $(3)$ into $(1)$,we get $A + 172 = 252$,so $A = 252 - 172 = 80 	ext{ years}$.

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