A book vendor sold a book at a loss of 20%. Had he sold

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A book vendor sold a book at a loss of 20%. Had he sold it for $ 108 more, he would have earned a profit of 30%. Find the cost price of the book?

If the cost price of the book be $ y, then
According to question ,

∴		y × ( 100 - 20 )	+ 108 =	y × ( 100 + 30 )
		100		100

⇒	13y	-	4y	= 108
	10		5

⇒	13y -8y	= 108
	10

⇒	5y	= 108 ⇒ y = $ 216
	10

Using the given formula :
Here, a = 20%, R = $ 108, b = 30%

C.P. =	R × 100
	b + a

C.P. =	108 × 100
	30 + 20

C.P. =	10800	= $ 216
	50