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

Update:

any idea how to use interpolation? Relevance
• 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.

• 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.