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
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) (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)
Solve: We'll use substitution. After moving 1*b to the right, we get: , or . Substitute that
into another equation: and simplify: So, we know that b=30. Since , a=-0.13.
Answer: .
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