When a person aged 39 is added to a group of n people, the average age increases by 2. When a person aged 15 is added instead, the average age decreases by 1. What is the value of W?
Choose the most appropriate option
A) 7	B) 8	C) 9	D) 10	E) 11
A simple and elegant solution.   As addition of 39, shifts mean by 2, and addition of 15, shifts mean by 1 to the other side, we have the mean lying between 3915, and in a ratio of 2:1   39-15= 
<gadget id="calculator">39-15</gadget>
<output>24</output>
24   24 divide by 3 is 8.   Meaning mean of the n terms is 15+8= 39-16= 
<gadget id="calculator">39-16</gadget>
<output>23</output>
23   Now, from first statement, When a person aged 39 is added to a group of n people, the average age increases by 2.   W*23 +39= 25*(W+1)   W = 7   Ans. (7)
<result>A</result>
When a person aged 39 is added to a group of n people, the average age increases by 2. When a person aged 15 is added instead, the average age decreases by 1. What is the value of W?