If the profit percent got on selling an article is numerically

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If the profit percent got on selling an article is numerically equal to its cost price in rupees and the selling price is $ 39, then cost price (in $) will be

1. 20
2. 22
3. 28
4. 30

Correct Option: D

Let the CP of the article be y
Gain % = y%

∴	39 - y	× 100 = y
	y

⇒ 3900 – 100y = y²
⇒ y² + 100y – 3900 = 0
⇒ y² + 130y – 30y – 3900 = 0
⇒ y(y + 130) – 30 (y + 130) = 0
⇒ (y – 30) (y + 130) = 0
⇒ y = 30 as y cannot be negative