Dan's equation is wrong.
Explanation:
Given, Dan borrows money to buy a new trumpet $400 at simple interest rate of 5% .
here P =$400, r = 5% and t = 1
![=\$(400 * 5 * 1)/(100)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/1derzowui46o5auz2ch9wk759e0qu1eh4t.png)
![=\$(0.05* 400)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/2akbwmv37an3cfeg0iigwyc9h6mh46gdhn.png)
Therefore he will need to pay back after one year is = 400+(0.05×400)
So, t = 400+(0.05×400)
Dan's equation is wrong.