Convert fractions to decimals using division and by changing the denominator to a power of ten.

$$
\frac{5}{8} = 5 \div 8 = 0.625
$$
The decimal is $\boxed{\text{0.625}}$.

• b) $\frac{17}{50}$

$$
\frac{17}{50} = 17 \div 50 = 0.34
$$
The decimal is $\boxed{\text{0.34}}$.

• c) $\frac{9}{20}$

$$
\frac{9}{20} = 9 \div 20 = 0.45
$$
The decimal is $\boxed{\text{0.45}}$.

2. Express each of the following into decimals by first changing the denominator into a power of ten.

• a) $\frac{1}{5}$

$$
\frac{2}{10} = 0.2
$$
The decimal is $\boxed{\text{0.2}}$.

• b) $\frac{3}{4}$

$$
\frac{75}{100} = 0.75
$$
The decimal is $\boxed{\text{0.75}}$.

• c) $\frac{24}{50}$

$$
\frac{48}{100} = 0.48
$$
The decimal is $\boxed{\text{0.48}}$.

3. Express each of the following as fractions.

• a) 0.6

$$
\frac{6 \div 2}{10 \div 2} = \frac{3}{5}
$$
The fraction is $\boxed{\frac{3}{5}}$.

• b) 2.27

$$
2.27 = 2 + \frac{27}{100} = \frac{200}{100} + \frac{27}{100} = \frac{227}{100}
$$
The fraction is $\boxed{\frac{227}{100}}$.

• c) $0.4\overline{15}$

$$
\frac{411 \div 3}{990 \div 3} = \frac{137}{330}
$$
The fraction is $\boxed{\frac{137}{330}}$.

4. Express each of the following as decimals.

• a) $\frac{2}{9}$

$$
\frac{2}{9} = 2 \div 9 = 0.222...
$$
The decimal is $\boxed{0.\overline{2}}$.

• b) $\frac{1}{6}$

$$
\frac{1}{6} = 1 \div 6 = 0.1666...
$$
The decimal is $\boxed{0.1\overline{6}}$.

• c) $\frac{3}{7}$

$$
\frac{3}{7} = 3 \div 7 = 0.428571428571...
$$
The decimal is $\boxed{0.\overline{428571}}$.

5. Round off the following numbers correct to 1 decimal place.

• a) 25.78

Since 8 is 5 or greater, round up the first decimal place. $25.78 \approx 25.8$ The rounded number is $\boxed{\text{25.8}}$.

• b) 0.946

Since 4 is less than 5, keep the first decimal place as it is. $0.946 \approx 0.9$ The rounded number is $\boxed{\text{0.9}}$.

• c) 199.994

Since 9 is 5 or greater, round up the first decimal place. Rounding 9 up results in a carry-over. $199.994 \approx 200.0$ The rounded number is $\boxed{\text{200.0}}$.

6. Round off the following numbers to the nearest hundredths.

• a) 3.9623

Since 2 is less than 5, keep the hundredths place as it is. $3.9623 \approx 3.96$ The rounded number is $\boxed{\text{3.96}}$.

• b) 19.9984

Since 8 is 5 or greater, round up the hundredths place. Rounding 9 up results in a carry-over to the tenths place, which also carries over to the units place. $19.9984 \approx 20.00$ The rounded number is $\boxed{\text{20.00}}$.

• c) 23.5675

Since 7 is 5 or greater, round up the hundredths place. $23.5675 \approx 23.57$ The rounded number is $\boxed{\text{23.57}}$.