Add all combinations of positive and negative \(5\) and \(7\).

Subtract \(-3\) from \(-9\).

Add \(-4\) to the difference of \(-2\) and \(5\).

Multiply all combinations of positive and negative \(7\) and \(3\).

Divide each of the following:

1. \(\dfrac{6}{3}\)

2. \(\dfrac{6}{-3}\)

3. \(\dfrac{-6}{3}\)

4. \(\dfrac{-6}{-3}\)

Simplify \((-2-3)(5-9)\)

Simplify \(2-5(7-4)-6\)

Simplify: \(\dfrac{-8-8}{-5-3}\)

Simplify: \(\dfrac{-5(-4)+2(-3)}{2(-1)-5}\)

Simplify the expression \(\dfrac{68-72}{5}\)

Simplify: \(3(2y-1)+y\)

Divide \(\dfrac{3}{4}\div\dfrac{6}{11}\) and reduce to lowest terms.

Divide \(10\div\dfrac{5}{6}\) and reduce to lowest terms.

Divide: \(-\dfrac{3}{8}\div 6\)

Add: \(\dfrac{5}{12}+\dfrac{7}{18}\)

Evaluate the expressions \((a+4)^2\), \(a^2+16\), and \(a^2+8a+16\) when \(a\) is \(-2\), \(0\), and \(3\).

Evaluate \(\dfrac{x-\mu}{\sigma}\) if \(x=25\), \(\mu=27.4\), and \(\sigma=4.8\).

Evaluate the expression \(\dfrac{s_1^2}{n_1}+\dfrac{s_2^2}{n_2}\) for the given values of the variables.

1. \(s_1=3\), \(s_2=4\), and \(n_1=n_2=100\)

2. \(s_1=1.2\), \(s_2=1.6\), and \(n_1=n_2=100\)

3. \(s_1=2.5\), \(s_2=3.8\), \(n_1=200\) and \(n_2=100\)