To find out how far Elena ran when she stopped at 2/3 of the way, we need to calculate 2/3 of 7/8 of a mile.
We can multiply the two fractions together:
\[ \text{Distance run} = \frac{2}{3} \times \frac{7}{8} \]
To multiply these fractions, multiply the numerators and the denominators:
\[ \text{Distance run} = \frac{2 \times 7}{3 \times 8} = \frac{14}{24} \]
Now, we can simplify \(\frac{14}{24}\). The greatest common divisor (GCD) of 14 and 24 is 2. So we divide both the numerator and the denominator by 2:
\[ \frac{14 \div 2}{24 \div 2} = \frac{7}{12} \]
Therefore, Elena ran \(\frac{7}{12}\) of a mile when she stopped for water.