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Algebra / Linear functions Difficulty: Medium

The boiling point of water at sea level is 212 degrees Fahrenheit $degrees Fahrenheit$ . For every 550 feet above sea level, the boiling point of water is lowered by about $1 degree Fahrenheit$ . Which of the following equations can be used to find the boiling point B of water, in $degrees Fahrenheit$ , x feet above sea level?

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Explanation

Choice D is correct. It’s given that the boiling point of water at sea level is 212°F and that for every 550 feet above sea level, the boiling point of water is lowered by about 1°F. Therefore, the change in the boiling point of water x feet above sea level is represented by the expression $the negative of the fraction x over 550$ . Adding this expression to the boiling point of water at sea level gives the equation for the boiling point B of water, in °F, x feet above sea level: $B equals, the negative of the fraction x over 550, end fraction, plus 212$ , or $B equals, 212 minus, the fraction x over 550$ .

Choices A and B are incorrect and may result from using the boiling point of water at sea level as the rate of change and the rate of change as the initial boiling point of water at sea level. Choice C is incorrect and may result from representing the change in the boiling point of water as an increase rather than a decrease.