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phil has saved some money and is going to buy some DVDs. The number N of DVDs Phil can buy is inversely proportional to the cost C of a DVD. If the cost of one DVD is $16, then he can buy 10. If the cost of one DVD is $20, then how many DVDs can he buy?

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Answer: He can buy 8 DVD's.

Explanation:

Since, The number N of DVDs Phil can buy is inversely proportional to the cost C of a DVD.

Thus,
N \propto (1)/(C)


N = (k)/(C) ------- (1)

Where k is the proportional constant.

And, According to the question,

If the cost of one DVD is $16, then he can buy 10 DVD,

That is, If C = $16 then N = 10

Put these value in equation (1),


10 = (k)/(16)

⇒ k = 160

Thus, the relation between N( number of DVD's ) and C( Cost of DVD's ) is, ( By putting the value of k in equation (1) )


N = (160)/(C)

If C = $20,


N = (160)/(20) = 8

Therefore, If the cost of one DVD is $20, he can buy 8 DVD's.

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