Question

bobs cell phone plan costs $29.99 a month for 350 minutes. he is charged for minute over 350 he uses. bobs bill last month was $85.29. how many minutes over 350 did he use last month? type your answer

Explanation:

Step1: Find the cost of extra - minutes

The base cost of the plan is $29.99. Bob's total bill was $85.29. So the cost of the extra - minutes is the total bill minus the base cost. Let $C_{extra}$ be the cost of extra - minutes.
$C_{extra}=85.29 - 29.99=55.3$

Step2: Assume the cost per extra - minute

Let's assume the cost per extra - minute is $x$. We need to find out how many extra - minutes he used. Let the number of extra - minutes be $n$.
We know that $C_{extra}=n\times x$. Usually, we need to know the cost per extra - minute. If we assume the cost per extra - minute is $0.45$ (a common value for over - minute charges in some plans).
$n=\frac{C_{extra}}{x}=\frac{55.3}{0.45}\approx122.89$

Answer:

If the cost per extra - minute is $0.45$, Bob used approximately 123 extra minutes.