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After replacing an old member by a new member, it was found that the average age of five members of a club is the same assit was $3 \,year$ ago. The difference between the ages of the replaced and the new member is ? (in $year$)
A
$2$
B
$4$
C
$8$
D
$15$
Solution
Let the average of $5$ person be $10 \,year.$
Then, sum of their age $=5 \times 10=50$ year
Average age of $5$ member $3$ year ago
$=\frac{50-3 \times 5}{5}+=7$ $year$
So after Adding the new member average become $7 year.$
Difference in the age of old member and New member $=5 \times 10-7 \times 5=15$ $year.$
Standard 13
Quantitative Aptitude
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