Suppose contact lenses cost $300 for a years supply or $30 for a months supply. Which is less expensive to order per year, paying for 13 months at one time or paying for one month at a time?

Answer 1

If a year's supply of contact lenses costs $300, then buying them monthly would cost $30 x 12 months = $360 per year.
Therefore, paying for 13 months at one time is less expensive at $300 compared to $360 if paid monthly.