Percentage of a number

Question

How can we find out what percentage 2 gigabytes is of 15 gigabytes?

I am not calculating correctly: 2 gb * x (percentage) = 15 gb x = 15/2

Answer 1

Let's use the Rule of Three:

The percentage must be to $100$ what $2$ is to $15$. Now $2$ is to $15$ what $\dfrac2{15}$ is to $1$, which is turn is what $\dfrac{200}{15}$ is to $100$. Hence the simplified answer is $\dfrac{40}3\approx13.33\,\%$.

Answer 2

You're working backwards. You want to find the % of 15, so it's 15*x = 2, or x = 2/15