How to calculate the missing value of energy consumption in the table?

Update:

any idea how to use interpolation?

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2 Answers

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  • 3 months ago

    The missing month is half way between the two known months. March is between 480 and 420, sounds like 450 is the answer.  May is half way between 420 and 470, making 445 the midpoint.

  • 3 months ago

    Linear Interpolation Between Two Known Points

    Put the months on the x-axis, but change Jan - Dec to 1 - 12.

    If the two known points are given by the coordinates (x2, y2) and (x4, y4),

    the linear interpolant is the straight line between these points. For a value 

    x3 in the interval (x2, x4), the value y3 along the straight line is given from the

    equation of slopes:

    (y3 - y2) / (x3 - x2) = (y4 - y2) / (x4 - x2)

    x2 = 2

    y2 = 480

    x3 = 3

    y3 = unknown

    x4 = 4

    y4 = 420

    (y3 - y2) / (x3 - x2) = (y4 - y2) / (x4 - x2)

    (y3 - y2) = (x3 - x2)(y4 - y2) / (x4 - x2)

    y3 = [(x3 - x2)(y4 - y2) / (x4 - x2)] + y2

    y3 = [(3 - 2)(420 - 480) / (4 - 2)] + 480

    y3 = [(1)(-60) / (2)] + 480

    y3 = [-60 / (2)] + 480

    y3 = -30 + 480

    y3 = 450 kWh

    The remaining interpolation is left as an exercise for the student.

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