The average of x numbers is y and average of y numbers is x. Then the average of all the numbers taken together is
Options:
A . $\text"x+y"/\text"2xy"$
B . $\text"2xy"/\text"x+y"$
C . $(x^2+y^2)/\text"x+y"$
D . $\text"xy"/\text"x+y"$
Answer: Option B Answer: (b) Sum of x numbers = xy Sum of y numbers = xy ∴ Required average = ${xy+xy}/{x+y}$ = ${2xy}/{x+y}$ Aliter : Using Rule 10, Here, $n_1$ = x, $a_1$ = y $n_2$ = y, $a_2$ = x ∴ Average = ${n_1a_1+n_2a_2}/{n_1+n_2}$ = ${xy+yx}/{x+y}$ = ${2xy}/{x+y}$
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