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Bunuel
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Bunuel
If 2/z = 2/(z + 1) + 2/(z + 9) which of these integers could be the value of z?

(A) 0
(B) 1
(C) 2
(D) 3
(E) 4

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Using different values given in the answer,
Put z=3
2/3=2/4+2/2/12
2/3=1/2+1/6
2/3=2/3
LHS=RHS
Answer D
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Bunuel
If 2/z = 2/(z + 1) + 2/(z + 9) which of these integers could be the value of z?

(A) 0
(B) 1
(C) 2
(D) 3
(E) 4

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MANHATTAN GMAT OFFICIAL SOLUTION:

Solving for z algebraically in this problem would not be easy. Instead, we can follow the hint in the question (“which of these integers…”) and test each answer choice:

A. 2/0 = 2/1 +2/9 INCORRECT (Division by zero)
A. 2/1 = 2/2 +2/10 INCORRECT
A. 2/2 = 2/3 +2/11 INCORRECT
A. 2/3 = 2/4 +2/12 CORRECT
A. 2/4 = 2/5 +2/13 INCORRECT

The correct answer is D, because it contains the only value that makes the equation work. Notice how quickly this strategy worked in this case
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askhere
Answer is z= 3.
One could easily pick numbers and check this within a minute.

But if we can rewrite the equation as (1/z) - (1/z+1) = 1/z+9. One can see that the left hand side is 1/z(z+1)
(For example 1/4- 1/5 = 1/20; 1/3-1/4 = 1/12; 1/9 - 1/10 = 1/90)
So you get z(z+1) = z+9. Now one can easily see that z=3 (One can also see that LHS is always even so RHS has to be even.So z has to be odd)

Answer : D

Although your approach is perfectly fine but i think using the options and plugging in the values would be more easy in here.
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