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If P + 1Q\frac{1}{Q}Q1​ = 1 and Q + 1R\frac{1}{R}R1​ = 1, then what is PQR?
Question

If P + 1Q\frac{1}{Q} = 1 and Q + 1R\frac{1}{R} = 1, then what is PQR?

A.

-1

B.

2

C.

-2

D.

Cannot be calculated 

Correct option is A

Given:

P + 1Q\frac{1}{Q}​ = 1 and Q +1R\frac{1}{R}​ = 1,

We are to find the value of P × Q × R

Solution:

P+1Q=1=>P=11QQ+1R=1=>1R=1Q=>R=11QNow, compute P×Q×R:P×Q×R=(11Q)×Q×11Q=(Q1)×11Q=Q11Q=(1Q)1Q=1\begin{aligned}&\text{} \\&P + \frac{1}{Q} = 1 \Rightarrow P = 1 - \frac{1}{Q} \\&Q + \frac{1}{R} = 1 \Rightarrow \frac{1}{R} = 1 - Q \Rightarrow R = \frac{1}{1 - Q} \\[10pt]&\text{Now, compute } P \times Q \times R: \\&P \times Q \times R = \left(1 - \frac{1}{Q} \right) \times Q \times \frac{1}{1 - Q} \\[10pt]&= (Q - 1) \times \frac{1}{1 - Q} \\[10pt]&= \frac{Q - 1}{1 - Q} = \frac{- (1 - Q)}{1 - Q} = -1\end{aligned}

Correct Option: (A) -1

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