Final answer:
To determine the time period for which Dan's savings account was open, the simple interest formula was used. With an interest of $72, a principal of $300, and an annual rate of 4%, it was calculated that the account was open for 6 years.
Step-by-step explanation:
The student's question pertains to calculating the time period for which the savings account was open based on the simple interest earned. The formula for simple interest is Interest = Principal × Rate × Time, where Interest is the total interest earned, Principal is the initial amount deposited, Rate is the annual interest rate (expressed as a decimal), and Time is the number of years the account was open.
In this case, Dan earned $72 in interest on his initial deposit of $300 at an annual simple interest rate of 4% or 0.04. Using the simple interest formula I = P × R × T, we need to solve for T (Time in years). Substituting in the known values:
$72 = $300 × 0.04 × T
Divide both sides of the equation by ($300 × 0.04) to isolate T:
T = $72 / ($300 × 0.04) = $72 / $12 = 6
Therefore, the account was open for 6 years.