A diamond today cost ten dollars more than twice what it cost last year. The sum of the cost (last year and this year) is $2500. What is the cost of last year diamond? What are the reasonable domain and range?

The cost of the diamond last year is x = $ 830

Step-by-step explanation:

Let the cost of diamond last year = x

the cost of diamond present year = y

Given that diamond today cost ten dollars more than twice what it cost last year.

⇒ y = 2 x + 10   (1)

The sum of the cost (last year and this year) is  = $ 2500

⇒ x + y = $ 2500 (2)

Put the value of y in equation (2) from equation (1), we get

⇒ 2 x + 10 + x = $ 2500

⇒ 3 x = 2490

⇒ x = $ 830

& y = 2500 - 830

⇒ y = $ 1670

Therefore the cost of the diamond last year is x = $ 830

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