For each number of pennies below, arrange them first into a complete rectangular array and then into a different rectangular array that has a remainder of one (so there is one extra penny). Write an expression for each arrangement.

1. $10$ pennies

   Hint 1 (a):

   Try dividing $10$ by one or two to get your rectangle.

   Answer 1 (a):

   $\begin{array} {c c c c c} \bigcirc & \bigcirc & \bigcirc & \bigcirc & \bigcirc\\ \bigcirc & \bigcirc & \bigcirc & \bigcirc & \bigcirc\\ \end{array}$

   Hint 2 (a):

   To have a remainder of one, you want your rectangular array to be one less than $10$. That means you need to use the factors of $9$ to get a rectangle for it.

   Answer 2 (a):

   $\begin{array} {c c c c} \bigcirc & \bigcirc & \bigcirc\\ \bigcirc & \bigcirc & \bigcirc & \bigcirc\\ \bigcirc & \bigcirc & \bigcirc\\ \end{array}$

2. $15$ pennies

   Hint (b):

   This one is very similar to the previous problem. What numbers divide into $15$ evenly?

3. $25$ pennies

   Hint (c):

   This problem is very similar to the previous two. What numbers divide into $25$ evenly?