SOLUTION: The credit remaining on a phone card (in dollars) is a linear function of the total calling time made with the card (in minutes). The remaining credit after 43 minutes of calls is

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Question 941566: The credit remaining on a phone card (in dollars) is a linear function of the total calling time made with the card (in minutes). The remaining credit after 43 minutes of calls is $24.41, and the remaining credit after 82 minutes of calls is $19.34. What is the remaining credit after 103 minutes of calls?
Answer by srinivas.g(540) About Me  (Show Source):
You can put this solution on YOUR website!
Let y be Credit remaining and t be the time
assume y = at+b
where a, be are constants
when t= 43 min , y = $24.41
24.41 =a*43+b...........eq(1)
when t= 82 min , y= $19.34
19.34 = a*82+b....................eq(2)
Solved by pluggable solver: SOLVE linear system by SUBSTITUTION
Solve:
We'll use substitution. After moving 1*b to the right, we get:
43%2Aa+=+24.41+-+1%2Ab, or a+=+24.41%2F43+-+1%2Ab%2F43. Substitute that
into another equation:
82%2A%2824.41%2F43+-+1%2Ab%2F43%29+%2B+1%5Cb+=+19.34 and simplify: So, we know that b=30. Since a+=+24.41%2F43+-+1%2Ab%2F43, a=-0.13.

Answer: system%28+a=-0.13%2C+b=30+%29.

a=-0.13 , b =30
hence y= (-0.13)t+30
equation becomes y =-0.13t+30
when t = 103 min, y= -0.13*103 +30
= $16.61
Result:Remaining credit after 103 min = $ 16.61