Question 655419
You pull out the plug from the bathtub. After 40 seconds, there are 13 gallons of water left in the tub. One minute after you pull the plug, there are 10 gallons left. Assume that the number of gallons varies linearly with the time since the plug was pulled.
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They basically give you two points and they want you to find the equation of the line.
Note: 1 minute is 60 seconds
(40,13) and (60,10)
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slope = (y2-y1)/(x2-x1)
slope = (10-13)/(60-40)
slope = -3/20
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Using one point (60,10) and the slope above, plug into "point-slope" form:
y - y1 = m(x - x1)
y - 10 = (-3/20)(x - 60)
y - 10 = (-3/20)x - (-3/20)60
y - 10 = (-3/20)x - (-3)3
y - 10 = (-3/20)x - (-9)
y - 10 = (-3/20)x + 9
y = (-3/20)x + 19  (this is what they're looking for)