The charge for telephone calls T, is partly constant and partly varies with the number n of unit of call. The bill for 580 units of call is 900 .while the bill for 310 units is 500.
To solve this problem, we need to determine the constant and variable parts of the telephone call charges.
Let's assume the constant charge is represented by 'C' and the variable charge per unit of call is represented by 'V'.
Given the information, we can set up two equations:
1) For the bill of 580 units of call:
T = C + (580 * V)
900 = C + (580 * V) ---- (Equation 1)
2) For the bill of 310 units of call:
T = C + (310 * V)
500 = C + (310 * V) ---- (Equation 2)
We can now solve these two equations simultaneously to find the values of 'C' and 'V'.
First, let's isolate 'C' in both equations:
From Equation 1:
C = 900 - (580 * V) ---- (Equation 3)
From Equation 2:
C = 500 - (310 * V) ---- (Equation 4)
Now, equate Equation 3 and Equation 4 to find the value of 'V':
900 - (580 * V) = 500 - (310 * V)
900 - 500 = (310 * V) - (580 * V)
400 = -270 * V
V = -400 / -270
V ≈ 1.481
Now that we have the value of 'V', we can substitute it into either Equation 3 or Equation 4 to find the value of 'C'. Let's use Equation 3:
C = 900 - (580 * 1.481)
C ≈ 900 - 858.58
C ≈ 41.42
Therefore, the constant part of the telephone call charge is approximately 41.42 and the variable charge per unit of call is approximately 1.481.
think of it as being given 2 ordered pairs (580,900) and (310,500)
of the type (x,y) where x is number of units, and y is cost
slope = (900-500)/(580-310) = 400/270 = 40/27
y = mx + b is you slope y-intercept form
using one of the points, and the slope ...
900 = (40/27)(580) = b
b = 1100/27
y = (40/27)x + 1100/27
or
cost = (40/27)(number of items) + 1100/27
testing with the point not used, (310,500)
LS = 500
RS = (40/27)(310) + 1100/27 = 500
= LS
My answer is correct.