Question

Find the first term of the arithmetic sequence in which a_28=423/4 and the common difference is 5/4.

Answer 1

We have \[a_{28} = a_1 + 27d = \frac{423}{4}\] where $d = 5/4.$ Solving for $a_1,$ we have \[a_1 = \frac{423}{4} - 27 \cdot \frac{5}{4} = \boxed{\frac{18}{4} = \frac{9}{2}}.\]