The electricity bill of a certain establishment is partly fixed and partly variable depending on the number of units of electricity consumed. In a certain month when 540 units were consumed, the bill was Rs.1,800. In another month when 620 units were consumed, the bill was Rs.2,040. If in a month 500 units are consumed, then the bill for that month will be:

The bill has a fixed part and a variable part (dependent on units consumed).

When 540 units are consumed, the bill = Rs. 1800.

When 620 units are consumed, the bill = Rs. 2040.

Total Bill = Fixed Charge + (Variable Charge per Unit × Number of Units Consumed)

Let the fixed charge be F and the variable charge per unit be V.

For 540 units:

F + 540V = 1800………..(i)

For 620 units:

F + 620V = 2040………….(ii)

Subtract the first equation from the second:

(F + 620V) - (F + 540V) = 2040 – 1800

80V = 240

V = 3

Substituting V = 3 into the first equation:

F + 540 × 3 = 1800

F + 1620 = 1800

F = 1800 – 1620 = 180

Now, the bill for 500 units:

Total Bill = F + 500 × V = 180 + 500 × 3=180 + 1500 = Rs.1680