# If the cost of bananas is increased by Rs. 10 per dozen, one can get 3 dozen less for Rs.600.

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If the cost of bananas is increased by Rs. 10 per dozen, one can get 3 dozen less for Rs.600. Find the original cost of one dozen of bananas

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Let x be the original cost of 1 dozen bananas , for Rs. 600 we  gets y dozens.

xy =600 .................... {1}

$$y={600\over x}$$

By increasing the cost of 1 dozen of bananas by Rs. 10 we get 3 dozen less bananas

(x +10)(y - 3)=600  ..........................{2}

Substituting the y value in (2), we get

$$(x+10)({600\over x}-3)=600$$

$$(x+10)({(600-3x)\over x})=600$$

$$6000-30x-3x^2=0$$

$$3(x^2+10x-2000)=0$$

$$(x^2+10x-2000)=0$$

(x+50)(x-40)=0

x=-50 or 40

Since cost of bananas cannot be negative, x = 40. So, the original cost of one dozen of bananas is Rs.40