How do you solve  1/2a-1<8?

$a < 18$
We begin with $\frac{1}{2} a - 1 < 8$. From here, we will just add $1$ on both sides to give us $\frac{1}{2} a < 9$. Now we just divide by $\frac{1}{2}$ on both sides. That leaves us with $a < 18$.