Solve all the questions from 1 to 19

$$18 - 12 = 6$$

The answer is $\boxed{\textbf{6}}$.

$$12 + 5 = 17$$

The answer is $\boxed{\textbf{17}}$.

$$4 \times 8 = 32$$

The answer is $\boxed{\textbf{32}}$.

$$5 - 3 = 2$$

The answer is $\boxed{\textbf{2}}$.

$$10 + 14 - 4 = 24 - 4 = 20$$

The answer is $\boxed{\textbf{20}}$.

$$36 \div 6 = 6$$

The answer is $\boxed{\textbf{6}}$.

$$40 - 20 = 20$$

The answer is $\boxed{\textbf{20}}$.

$$100 - 40 = 60$$

The answer is $\boxed{\textbf{60}}$.

The least common multiple of 2 and 4 is 4.

$$\frac{1}{2} + \frac{1}{4} = \frac{1 \times 2}{2 \times 2} + \frac{1}{4} = \frac{2}{4} + \frac{1}{4}$$

$$\frac{2}{4} + \frac{1}{4} = \frac{2 + 1}{4} = \frac{3}{4}$$

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

The least common multiple of 5 and 10 is 10.

$$\frac{3}{5} - \frac{1}{10} = \frac{3 \times 2}{5 \times 2} - \frac{1}{10} = \frac{6}{10} - \frac{1}{10}$$

$$\frac{5}{10} = \frac{1}{2}$$

The answer is \boxed{\textbf{\frac{1}{2}}}.

$$\frac{6}{12} = \frac{1}{2}$$

The answer is \boxed{\textbf{\frac{1}{2}}}.

$$\frac{15}{6} = \frac{5}{2}$$

The answer is \boxed{\textbf{\frac{5}{2}}}.

$$0.75 + 0.25 = 1.00$$

The answer is $\boxed{\textbf{1}}$.

$$1.5 - 0.8 = 0.7$$

The answer is $\boxed{\textbf{0.7}}$.

$$2.3 \times 4 = 9.2$$

The answer is $\boxed{\textbf{9.2}}$.

$$6.4 \div 2 = 3.2$$

The answer is $\boxed{\textbf{3.2}}$.

$$3^2 = 9$$ $$4^2 = 16$$

$$9 + 16 = 25$$

The answer is $\boxed{\textbf{25}}$.

$$\sqrt{25} = 5$$ $$\sqrt{16} = 4$$

$$5 + 4 = 9$$

The answer is $\boxed{\textbf{9}}$.

$$25 - 10 = 15$$

The answer is $\boxed{\textbf{15}}$.