# 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

Anurag Mishra Professor Asked on 19th April 2016 in

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.

Anurag Mishra Professor Answered on 24th April 2016.