SOLUTION: Hello, i have problem on a word problem for linear equation. hope you can help me When making a telephone call using a calling card, a call lasting 5 minutes costs$1.45. A call

Algebra ->  Linear-equations -> SOLUTION: Hello, i have problem on a word problem for linear equation. hope you can help me When making a telephone call using a calling card, a call lasting 5 minutes costs$1.45. A call      Log On


   

Question 1097145: Hello, i have problem on a word problem for linear equation. hope you can help me
When making a telephone call using a calling card, a call lasting 5 minutes costs$1.45. A call lasting 15 minutes costs $3.45. Let y be the cost of making a call lasting x minutes using a calling card. Write a linear equation that models the cost of making a call lasting x minutes.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Actually, you are given 2 points on a line, and
since 2 points dfine a line, you can plot the line.
The points are:
( 5, 1.45 )
( 15, 3.45 )
Use the general point-slope formula
+%28+y+-+1.45+%29+%2F+%28+x+-+5+%29+=+%28+3.45+-+1.45+%29+%2F+%28+15+-+5+%29+
+%28+y+-+1.45+%29+%2F+%28+x+-+5+%29+=+2+%2F+10+
+%28+y+-+1.45+%29+%2F+%28+x+-+5+%29+=+1+%2F+5+
Multiply both sides by +5%2A%28+x+-+5+%29+
+5%2A%28+y+-+1.45+%29+=+x+-+5+
+5y+-+7.25+=+x+-+5+
+5y+=+x+%2B+2.25+
+y+=+%281%2F5%29%2Ax+%2B+.45+
+y+=+.2x+%2B+.45+
-------------------------------
check:
does it go through ( 5, 1.45 ) ?
+1.45+=+.2%2A5+%2B+.45+
+1.45+=+1.45+
OK
check ( 15, 3.45 )
+3.45+=+.2%2A15+%2B+.45+
+3.45+=+3.45+
OK