# The electricity bill of a certain establishment is partly fixed and partly varies with the number

The electricity bill of a certain establishment is partly fixed and partly varies with the number of units of electricity In a certain month when 540 units are consumed, the bill is Rs. 1,800. In another month the consumed units are 620 and the bill is Rs. 2,040.If 500 units of electricity is consumed in a month, the bill for that month is

(1) Rs. 1,560

(2) Rs. 1,600

(3) Rs. 1,620

(4) Rs. 1,680

**Answer: (4) Rs.1,680 **

**Solution:-**

Let the fixed amount be Rs. x and the cost of each unit be Rs. y.

Then,

540y + x = 1800 …(i) and

620y + x = 2040 …(ii)

On subtracting (i) from (ii), we get 8O7 = 240 <=> y = 3.

Putting y = 3 in (i), we get :

540 x 3 + x = 1800 <=> x = (1800 – 1620) = 180.

Therefore, Fixed charges = Rs. 180, Charge per unit = Rs. 3.

Total charges for consuming 500 units = Rs. (180 + 500 x 3) = Rs. 1680.

Hence, the correct answer is option (4) Rs.1,680.