Write a sum for the number lines below and calculate the answers. Draw number lines for the following sums.

The line from 0 to 1 is divided into 4 equal parts, so each part is $\frac{1}{4}$.

It covers 2 parts, so it represents $\frac{2}{4}$.

It covers 1 part, so it represents $\frac{1}{4}$.

The sum is $\boxed{\frac{2}{4} + \frac{1}{4} = \frac{3}{4}}$.

c)

The line from 0 to 1 is divided into 3 equal parts, so each part is $\frac{1}{3}$.

It covers 1 part, so it represents $\frac{1}{3}$.

It covers 1 part, so it represents $\frac{1}{3}$.

The sum is $\boxed{\frac{1}{3} + \frac{1}{3} = \frac{2}{3}}$.

d)

The line from 0 to 1 is divided into 5 equal parts, so each part is $\frac{1}{5}$.

It covers 2 parts, so it represents $\frac{2}{5}$.

It covers 2 parts, so it represents $\frac{2}{5}$.

The sum is $\boxed{\frac{2}{5} + \frac{2}{5} = \frac{4}{5}}$.

e)

The line from 0 to 1 is divided into 6 equal parts, so each part is $\frac{1}{6}$.

It covers 3 parts, so it represents $\frac{3}{6}$.

It covers 2 parts, so it represents $\frac{2}{6}$.

The sum is $\boxed{\frac{3}{6} + \frac{2}{6} = \frac{5}{6}}$.

4. Draw number lines for the following sums.

a) $\frac{1}{4} + \frac{2}{4} =$

Mark the points $\frac{1}{4}$, $\frac{2}{4}$, $\frac{3}{4}$, and 1 (or $\frac{4}{4}$).

The number line should look like this:

0 ---|---|---|---|--- 1
    1/4 2/4 3/4
    <-----> (1/4)
        <-----> (2/4)

The answer is $\boxed{\frac{3}{4}}$.

b) $\frac{1}{2} + \frac{1}{4} =$

The common denominator for 2 and 4 is 4.

Mark the points $\frac{1}{4}$, $\frac{2}{4}$ (or $\frac{1}{2}$), $\frac{3}{4}$, and 1 (or $\frac{4}{4}$).

The number line should look like this:

0 ---|---|---|---|--- 1
    1/4 2/4 3/4
    <---------> (1/2 or 2/4)
            <---> (1/4)

The answer is $\boxed{\frac{3}{4}}$.

Problem solving:
A chocolate cake is cut into 30 pieces. If a fifth has been eaten, how many pieces are left?

There are $\boxed{24}$ pieces left.