Add the following rational numbers: a) -2/5 and 4/5, b) -7/3 and 1/3, c) -11/8 and 5/8, d) -6/11 and -4/11, e) 5/6 and -1/6, f) [omitted]

$$= \frac{2}{5}$$

The sum is $\boxed{\frac{2}{5}}$.

b) $\frac{-7}{3}$ and $\frac{1}{3}$

$$= -2$$

The sum is $\boxed{-2}$.

c) $\frac{-11}{8}$ and $\frac{5}{8}$

$$= \frac{-3}{4}$$

The sum is $\boxed{\frac{-3}{4}}$.

d) $\frac{-6}{11}$ and $\frac{-4}{11}$

$$= \frac{-10}{11}$$

The sum is $\boxed{\frac{-10}{11}}$.

e) $\frac{5}{6}$ and $\frac{-1}{6}$

$$= \frac{2}{3}$$

The sum is $\boxed{\frac{2}{3}}$.

f) $\frac{-17}{15}$ and $\frac{-1}{15}$

$$= \frac{-6}{5}$$

The sum is $\boxed{\frac{-6}{5}}$.

2. Add the following rational numbers:

a) $\frac{3}{4}$ and $\frac{-3}{5}$

$$= \frac{3}{20}$$

The sum is $\boxed{\frac{3}{20}}$.

b) $\frac{5}{8}$ and $\frac{-7}{12}$