Question

suppose a 5 minute overseas call costs 5.91 and a 10 minute call costs 10.86. the cost of the call and length of the call are related. the cost of each minute is constant. How long can you talk on th phone if you only have 12.00 to spend on the call?

Answer 1

$\begin{gathered} We\text{ will construct an equation} \\ y=mx+b \\ \text{where y is the cost and x is the minute} \\ \\ m=\frac{10.86-5.91}{10-5} \\ m=\frac{4.95}{5} \\ m=0.99 \\ \\ \text{ and now} \\ \\ 5.91=0.99\cdot5+b \\ \\ 5.91=4.95+b \\ b=5.91-4.95 \\ b=0.96 \\ \\ y=0.99x+b \\ \text{if we have 12 to spend} \\ \\ 12=0.99x+0.96 \\ 12-0.96=0.99x \\ 11.04=0.99x \\ x=\frac{11.04}{0.99} \\ x=11.15 \\ \\ \\ \text{ Now we can only talk approximately 11 minutes!} \end{gathered}$