SOLUTION: The height (in centimeters) of a candle is a linear function of the amount of time (in hours) it has been burning. When graphed, the function gives a line with a slope of -0.4. S

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: The height (in centimeters) of a candle is a linear function of the amount of time (in hours) it has been burning. When graphed, the function gives a line with a slope of -0.4. S      Log On


   

Question 1138789: The height (in centimeters) of a candle is a linear function of the amount of time (in hours) it has been burning. When graphed, the function gives a line with a slope of -0.4.
Suppose that the height of the candle after 13 hours is 18.8 centimeters. What will be the height of the candle after 21 hours?
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39621) About Me  (Show Source):
You can put this solution on YOUR website!
point (13, 18.8)
slope -4

y-18.8=-4%28x-13%29
y=-4%28x-13%29%2B18.8

for the question, let x=21 and evaluate y.

Answer by ikleyn(52818) About Me  (Show Source):
You can put this solution on YOUR website!
.

point  (13, 18.8)

slope  -0.4


    y - 18.8 = -0.4*(x-13)

    y = -0.4*(x-13) + 18.8


After 21 hours the height will be

    y = -0.4*(21 - 13) + 18.8 = 15.6 centimeters.    ANSWER

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Notice that if you evaluate the height using formula from the @josgarithmetic post


    y = -4*(x-13) + 18.8 


you will get a negative height (!)


It is why I placed my solution here.