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Question

If xy = 9, yz = 16 and xz = 25, then what is the value of (x + y + z)?

A) 12.0
B)12.4
C)12.8
D)13.0

Comments

3 eqns are given with 3 unknowns.

solving them you will get, x=15/4, y=12/5, z=20/3

x+y+z = 12.816

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It should be option C. $12.82$

$x = \frac{9}{y} .... (1)$

$z = \frac{16}{y}..... (2)$

$z = \frac{25}{x}..... (3)$

comparing 2 and 3

$\frac{25}{9/y} = \frac{16}{y} = y^2 = \frac{16 \times 9}{25} = \frac{12}{5}$

substituting in other equations we get $x = \frac{45}{12} \ and \ z= \frac{80}{12}$

adding all we get $12.82$

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xy = 9 , yz = 16 , zx = 25

mutliyply you get  (xyz)$^2$ = 3600

xyz = 60  , now  using  these three xy = 9 , yz = 16 , zx = 25  

substitute x = $\frac{9}{y}$ in xyz = 60   , z  =$\frac{20}{3}$   

similarly find other values and add

Answer 1

We are considering only positive values because all the options are in positive.

Answer is C)