Question

The electricity bill of a certain establishment is partly fixed and partly varies as the number of units of electricity consumed. When in a certain month 540 units are consumed, the bill is Rs. 1800. In another month 620 units are consumed and the bill is Rs. 2040. In yet another month 500 units are consumed then, the bill for that month would be

• A. Rs. 1560
• B. Rs. 1680
• C. Rs. 1840
• D. Rs. 1950

Answer 1

The correct option is B Rs. 1680

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 $80y=240\Rightarrow y=3$
Putting y = 3 in (i), we get :
$540\times 3+x=1800\Rightarrow x=(1800-1620)=180$
$\therefore$ Fixed charges $=Rs.180,$ Charge per unit $=Rs.3$
Total charges for consuming $500$ units $=Rs.(180+500\times 3)=Rs.1680$