Let's solve each of these division problems.

1. $8 \frac{4}{5} \div 8$

Convert the mixed number to an improper fraction: $8 \frac{4}{5} = \frac{44}{5}$ Now, divide by 8 (which is equivalent to multiplying by the reciprocal of 8, i.e., $\frac{1}{8}$): $\frac{44}{5} \div 8 = \frac{44}{5} \times \frac{1}{8} = \frac{44}{40} = \frac{11}{10}$ So, the result is $\frac{11}{10}$ or 1.1.

2. $3 \frac{12}{15} \div \frac{10}{21}$

Convert the mixed number to an improper fraction: $3 \frac{12}{15} = 3 \frac{4}{5} = \frac{19}{5}$ Now divide by $\frac{10}{21}$, which is the same as multiplying by $\frac{21}{10}$: $\frac{19}{5} \div \frac{10}{21} = \frac{19}{5} \times \frac{21}{10} = \frac{399}{50}$ So, the result is $\frac{399}{50}$, or 7.98.

3. $12 \frac{8}{9} \div \frac{11}{15}$

Convert the mixed number to an improper fraction: $12 \frac{8}{9} = \frac{116}{9}$ Now divide by $\frac{11}{15}$, which is the same as multiplying by $\frac{15}{11}$: $\frac{116}{9} \div \frac{11}{15} = \frac{116}{9} \times \frac{15}{11} = \frac{1740}{99} = \frac{580}{33}$ So, the result is $\frac{580}{33}$, or approximately 17.58.

4. $15 \frac{6}{7} \div \frac{3}{5}$

Convert the mixed number to an improper fraction: $15 \frac{6}{7} = \frac{111}{7}$ Now divide by $\frac{3}{5}$, which is the same as multiplying by $\frac{5}{3}$: $\frac{111}{7} \div \frac{3}{5} = \frac{111}{7} \times \frac{5}{3} = \frac{555}{21} = \frac{185}{7}$ So, the result is $\frac{185}{7}$, or approximately 26.43.

5. $3 \frac{9}{10} \div 3$

Convert the mixed number to an improper fraction: $3 \frac{9}{10} = \frac{39}{10}$ Now divide by 3, which is the same as multiplying by $\frac{1}{3}$: $\frac{39}{10} \div 3 = \frac{39}{10} \times \frac{1}{3} = \frac{39}{30} = \frac{13}{10}$ So, the result is $\frac{13}{10}$, or 1.3.

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Would you like more details or explanations for any of these steps?

Here are 5 related questions:

1. How do you convert a mixed number to an improper fraction?
2. What are the steps to divide fractions?
3. How do you simplify complex fractions?
4. What is the importance of finding the reciprocal when dividing fractions?
5. How can you check if your fraction division result is correct?

Tip: When dividing by a whole number, it's helpful to think of it as multiplying by the reciprocal for easier calculation.