1. a) [[$ \frac{1}{-\frac{4}{25}}=-\frac{25}{4} \quad$]]​ b) [[$ -\left(-\frac{4}{25}\right)=\frac{4}{25} \quad $]]​ c) [[$ \left|-\frac{4}{25}\right|=\frac{4}{25} \quad $]]​ d) [[$ -\left(-\frac{4}{25}\right)^2=-\frac{16}{625} $]]​

2. a) [[$ 55 \cdot 99=55 \cdot 100 - 55= 5500-55=5445 $]]​

b) [[$ 4 \cdot 17+16 \cdot 17=(4+16)\cdot17=20\cdot17=20\cdot20-20\cdot3=400-60=340 $]]​

3. a) [[$ \frac{1}{2}+\frac{1}{3}=\frac{3}{6}+\frac{2}{6}=\frac{5}{6} $]]​

b) [[$ \frac{1}{2}-\frac{1}{3}=\frac{3}{6}-\frac{2}{6}=\frac{1}{6} $]]​

c) [[$ \frac{1}{2}\cdot\frac{1}{3}=\frac{1\cdot1}{2\cdot3}=\frac{1}{6} $]]​

d) [[$ \frac{1}{2}:\frac{1}{3}=\frac{1}{2}\cdot\frac{3}{1}=\frac{3}{2} $]]​

4. a) [[$ \, 3(x+1)=7 \\ 3x+3=7 \\ 3x=4 \\ x=\frac{4}{3}$]]​

b) [[$ \, \frac{x}{2}=\frac{x}{4}+2 \\ \frac{4x}{8}=\frac{2x}{8}+\frac{16}{8} \\ 4x=2x+16 \\ 2x=16 \\ x=8 $]]​

5. [[$ \,2x+1<4x+5 \\ -2x<4 \\ 2x>4 \\ x>2$]]​