If $x$ is a positive multiple of 8 and $x^2>100$, but $x<20$, what is $x$?
I need to find a positive multiple of 8 that satisfies two inequalities: $x^2>100$ and $x<20$. I can start by listing some multiples of 8: 8, 16, 24, 32, 40, and so on. I can see that 24, 32, and 40 are too big, since they are greater than 20. That leaves 8 and 16 as possible candidates. I can check if they satisfy the other inequality, $x^2>100$. I know that $8^2=64$ and $16^2=256$. I can see that 64 is not greater than 100, so 8 does not work. But 256 is greater than 100, so 16 does work. Therefore, $x=16$ is the only positive multiple of 8 that satisfies both inequalities. 