Try the following ACT math practice question that tests your understanding of arithmetic sequences.

The first four terms of an arithmetic sequence are $a, x, b, 2x$. The ratio of $a$ to $b$ is

1. $\quad \displaystyle \frac{1}{4}$
2. $\quad \displaystyle \frac{1}{3}$
3. $\quad \displaystyle \frac{1}{2}$
4. $\quad \displaystyle \frac{2}{3}$
5. $\quad 2$

Try the following ACT math practice question that tests your understanding of mixture questions.

How many liters of a $12$ percent alcohol solution must be added to $6$ liters of a $24$ percent alcohol solution to obtain a solution that is $15$ percent alcohol?

1. $\quad 9$
2. $\quad 15$
3. $\quad 18$
4. $\quad 20$
5. $\quad 24$