Add the following rational numbers:
(i) `5/11` and `4/11`, (ii) `-3/8` and `5/8`, (iii) `-6/13` and `8/13`, (iv) `-8/15` and `-7/15`, (v) `-13/20` and `17/20`, (vi) `-3/8` and `5/(-8)`

Answer

Let's solve the given rational number addition step by step.

### Step-by-Step Solution:

**(i) Add `5/11` and `4/11`:**
1. Since the denominators are the same, we can directly add the numerators.
\[ \frac{5}{11} + \frac{4}{11} = \frac{5 + 4}{11} = \frac{9}{11} \]

**(ii) Add `-3/8` and `5/8`:**
1. Again, the denominators are the same, so we add the numerators.
\[ \frac{-3}{8} + \frac{5}{8} = \frac{-3 + 5}{8} = \frac{2}{8} \]
2. Simplifying \(\frac{2}{8}\):
\[ \frac{2}{8} = \frac{1}{4} \]

**(iii) Add `-6/13` and `8/13`:**
1. The denominators are the same, so we add the numerators.
\[ \frac{-6}{13} + \frac{8}{13} = \frac{-6 + 8}{13} = \frac{2}{13} \]

**(iv) Add `-8/15` and `-7/15`:**
1. The denominators are the same, so we add the numerators.
\[ \frac{-8}{15} + \frac{-7}{15} = \frac{-8 - 7}{15} = \frac{-15}{15} \]
2. Simplifying \(\frac{-15}{15}\):
\[ \frac{-15}{15} = -1 \]

**(v) Add `-13/20` and `17/20`:**
1. The denominators are the same, so we add the numerators.
\[ \frac{-13}{20} + \frac{17}{20} = \frac{-13 + 17}{20} = \frac{4}{20} \]
2. Simplifying \(\frac{4}{20}\):
\[ \frac{4}{20} = \frac{1}{5} \]

**(vi) Add `-3/8` and `5/(-8)`:**
1. Rewrite \(5/(-8)\) as \(-5/8\):
\[ \frac{-3}{8} + \frac{-5}{8} = \frac{-3 - 5}{8} = \frac{-8}{8} \]
2. Simplifying \(\frac{-8}{8}\):
\[ \frac{-8}{8} = -1 \]

### Final Answers:
1. \( \frac{9}{11} \)
2. \( \frac{1}{4} \)
3. \( \frac{2}{13} \)
4. \( -1 \)
5. \( \frac{1}{5} \)
6. \( -1 \)