Final answer:
The telephone bill is partly fixed and partly varies based on the number of calls consumed. By using two sets of data, we can solve for the fixed and variable components of the bill and calculate the bill for a different month. Option b is correct.
Step-by-step explanation:
The given problem is about a telephone bill that is partly fixed and partly varies depending on the number of calls consumed. We are given two sets of data - when 540 calls are made, the bill is Rs.1800, and when 620 calls are consumed, the bill is Rs.2040. From these two data points, we can form two equations to solve for the fixed and variable components of the telephone bill.
Let's assume the fixed component of the bill is represented by 'a' and the variable component is represented by 'b'.
From the first data point, we have the equation 540b + a = 1800.
From the second data point, we have the equation 620b + a = 2040.
Solving these two equations simultaneously will give us the values of 'a' and 'b'. Once we have these values, we can substitute them into the equation when 500 units are consumed to calculate the bill for that month.
In this case, the bill for that month would be Rs.1680.