10) (2)/(5)+(3)/(10)= II) (1)/(3)+(2)/(5)= 12) (3)/(5)+(2)/(4)=

10) To add fractions, they must have the same denominator. The least common multiple of 5 and 10 is 10. So, convert $\frac {2}{5}$ to a fraction with 10 as the denominator by multiplying both the numerator and the denominator by 2. This gives $\frac {4}{10}$. Now you can add the fractions: $\frac {4}{10}+\frac {3}{10}=\frac {7}{10}$.<br /><br />(1) Again, to add fractions, they must have the same denominator. The least common multiple of 3 and 5 is 15. Convert $\frac {1}{3}$ to a fraction with 15 as the denominator by multiplying both the numerator and the denominator by 5. This gives $\frac {5}{15}$. Similarly, convert $\frac {2}{5}$ to a fraction with 15 as the denominator by multiplying both the numerator and the denominator by 3. This gives $\frac {6}{15}$. Now you can add the fractions: $\frac {5}{15}+\frac {6}{15}=\frac {11}{15}$.<br /><br />12) The least common multiple of 5 and 4 is 20. Convert $\frac {3}{5}$ to a fraction with 20 as the denominator by multiplying both the numerator and the denominator by 4. This gives $\frac {12}{20}$. Similarly, convert $\frac {2}{4}$ to a fraction with 20 as the denominator by multiplying both the numerator and the denominator by 5. This gives $\frac {10}{20}$. Now you can add the fractions: $\frac {12}{20}+\frac {10}{20}=\frac {22}{20}$. Simplify this fraction by dividing both the numerator and the denominator by 2 to get $\frac {11}{10}$.