The telephone bill of a certain establishment is party fixed and partly varies as the number of calls consumed. When in a certain month 540 calls made the bill is Rs.1800. In another month 620 calls are consumed then the bill becomes Rs.2040. In another month 500 units are consumed due to more holidays. The bill for that month would be :

 The telephone bill of a certain establishment is party fixed and partly varies as the number of calls
     consumed. When in a certain month 540 calls made the bill is Rs.1800. In another month 620 calls are
     consumed then the bill becomes Rs.2040. In another month 500 units are consumed due to more
     holidays. The bill for that month would be :

a) Rs.1560           b) Rs.1680      c) 1840            d) Rs.1950

















 Expl : Let the fixed amount be Rs. X and the cost of each unit be Rs. Y.

    Then, 540y + x = 1800 …. And 620y + x =  2040

    On subtracting (i) from (ii), we get 80y = 240 -> y = 3

    Putting y = 3 in (i) we get :

    540 * 3 +  x = 1800 x = (1800-1620) = 180

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

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