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Answer:
In February, 423 daytime minutes is used
Step-by-step explanation:
Let the base plan charges be x
And cost per daytime minute be y
In December,
x + 510y = 92.25------------------(1)
In January,
x + 397y = 77.56---------------------(2)
Subtracting eq(2) from eq(1)
x + 510y = 92.25
x + 397y = 77.56
-------------------------------
0 + 113y = 14.69
-------------------------------
y = \frac{14.69}{113}
y = 0.13----------------------------------(3)
Substituting (3) in (1)
x + 510(0.13) = 92.25
x + 66.3 = 92.25
x = 92.25 - 66.3
x = 25.95
So In February
base plan + (daytime minute)(cost per daytime minute) = 80.9
25.95 + (daytime minute)(0.13) = 80.9
(daytime minute)(0.13) = 80.9 - 25.95
(daytime minute)(0.13) = 54.95
(daytime minute) =[tex]\frac{54.95}{0.13}[/tex]
daytime minutes = 422.69
daytime minute [tex]\approx 423[/tex]
The daytime minute did you use in February is 422.69
Given that
Your cell phone plan charges a base charge each month plus a charge per daytime minute of usage and December used 510 daytime minutes and your bill was 92.25 in January.
You only use 397 daytimes minutes and your bill was 77.56 in February your bill was 80.9.
We have to determine
How many daytime minutes-99 did you use in February?
According to the question
Let the base plan charges be x,
And the cost per daytime minute is y.
Charge per daytime minute of usage and December used 510 daytime minutes and your bill was 92.25 in January.
[tex]\rm x+510y = 92.25[/tex]
And you only use 397 daytimes minutes and your bill was 77.56 in February your bill was 80.9.
[tex]\rm x + 397y = 77.56[/tex]
Subtract equation 2 from equation 1
[tex]\rm x + 397y -(x + 510y) = 77.56- 92.25\\ \\ x + 397y -x -510y=-14.69\\\\ -113y =-14.69\\ \\ y = \dfrac{-14.69}{-113}\\ \\ y = 0.13[/tex]
Substitute the value of y in equation 1
[tex]\rm x+510y = 92.25\\ \\ \rm x+510(0.13) = 92.25\\\\ \rm x+66.3 = 92.25\\\\ x = 92.25 - 66.3\\\\ x =25.95[/tex]
Therefore,
The daytime minute did you use in February is,
Base plan + (daytime minute)(cost per daytime minute) = 80.9
[tex]\rm = 25.95 + (Daytime \ minute)(0.13) = 80.9\\\\ (Daytime\ minute)(0.13) = 80.9 - 25.95\\\\ (Daytime \ minute)(0.13) = 54.95\\ \\Daytime \ minute = \dfrac{54.95}{0.13}\\ \\ Daytime\ minute = 422.69[/tex]
Hence, The daytime minute did you use in February is 422.69.
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