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A person spent Rs $50000$ to produce a desktop computer and a laptop computer. He sold the desktop at $20\%$ profit and the laptop at $10\%$ loss. If overall he made a $2\%$ profit then the purchase price, in rupees, of the desktop is

Let the cost price (purchase price) of desktop and laptop be $x$ and $y$ respectively.

Now, $x + y = 50000 \quad \longrightarrow (1)$

And, $\frac{120}{100}x + \frac{90}{100}y = \frac{102}{100} \times 50000$

$\Rightarrow 12x + 9y = 102 \times 5000$

$\Rightarrow 12x + 9y = 510000$

$\Rightarrow 12x + 9(50000 – x) = 510000 \quad [\because \text{From equation} (1)]$

$\Rightarrow 12x + 450000 – 9x = 510000$

$\Rightarrow 3x = 60000$

$\Rightarrow \boxed{x = 20000}$

$\therefore$ The purchase price of the desktop is $₹ 20000.$

$\textbf{Short Method:}$ Using alligation method

The ratio of cost price (purchase price) $= 2 : 3$

$\therefore$ The desktop purchase price $= \frac{2}{5} \times 50000 = ₹ 20000.$

Correct Answer$: 20000$

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