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On 01/10/2013 10:38 AM, Hylton Conacher (ZR1HPC) wrote:

I am using Calc 3.4.5 on openSuSe Linux 11.2

I am working on a spreadsheet to cater for the monthly measurement of household electricity consumption, new unit purchase and costing of used units.

The electricity supplier gives me the first 150 units of electricity at R1.29 per unit. The next 350 units are costed at R1.35 per unit. Thereafter the units cost me R1.60 per unit. The monetary values per set amount of unit changes when the electricity provider increases prices i.e. the first 150 units might increase to R1.50 per purchased unit, the next 350 units might be costed at R1.55 and thereafter units will cost R2.00.

Each time I purchase electricity the units I am allocated are based on the above sliding scale starting from 0.

How can I work out the number of units I will receive for a given currency value i.e. R2000.00? i.e. x @ R1.29, y @ R1.35 and z @ R1.60= R2000

In addition how could I work out the value of units consumed using the above scale?

I am assuming the R values in the scale will change over time and these can each be averaged to calculate the cost of units used, but the problem is still to work out the formula.

Anybody have an idea if this is possible and where to start?

I am investigating results found on Google but would appreciate a pointer or three.

If I understand your problem, you have a general equation of ax + by + cz = d where a = 150, b = 350, c is currently unknown, d = 2000 (or any value you choose), x = 1.29, y = 1.35, and c = 1.60. Solving for c, you get c = (d - ax - by)/z.

Average cost per unit, ave, is ave = (a + b + c)/d., if I understand your question The value c must be calculated prior to this step. In terms of a Calc formula the c value would reference the cell with the previous calculation.

In your spreadsheet I would set a table with named cells for each value (a1 is Base_Rate and is 1.29, etc) so you can easily change the values and see the values used.

Jay Lozier

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