Solve the following mental maths problems: 1. \(sqrt(169) - sqrt(36)\) 2. \(2 x 3 x 5\) 3. \(10\% of 8000\) 4. \((15 - sqrt(25))2\) 5. \(3 x (18 + 27)\) 6. \(-19 x 0\) 7. \((60 + 132) / 12\) 8. \(6 x

Here are the solutions to the problems:

Mental Maths

1. Step 1: Calculate the square roots.

   $$\sqrt{169} = 13$$ $$\sqrt{36} = 6$$

   Step 2: Subtract the results.

   $$13 - 6 = \boxed{7}$$

2. Step 1: Multiply the numbers.

   $$2 \times 3 \times 5 = 6 \times 5 = \boxed{30}$$

3. Step 1: Convert the percentage to a decimal and multiply.

   $$10\% \text{ of } 8000 = 0.10 \times 8000 = \boxed{800}$$

4. Step 1: Calculate the square root inside the parentheses.

   $$\sqrt{25} = 5$$

   Step 2: Perform the subtraction inside the parentheses.

   $$(15 - 5)^2 = (10)^2$$

   Step 3: Square the result.

   $$(10)^2 = \boxed{100}$$

5. Step 1: Perform the addition inside the parentheses.

   $$(18 + 27) = 45$$

   Step 2: Multiply the result by 3.

   $$45 \times 3 = \boxed{135}$$

6. Step 1: Any number multiplied by zero is zero.

   $$-19 \times 0 = \boxed{0}$$

7. Step 1: Perform the addition inside the parentheses.

   $$(60 + 132) = 192$$

   Step 2: Divide the result by 12.

   $$192 \div 12 = \boxed{16}$$

8. Step 1: Perform the multiplication first (order of operations).

   $$6 \times 10 = 60$$

   Step 2: Add 1 to the result.

   $$60 + 1 = \boxed{61}$$

9. Step 1: Perform the multiplication first (order of operations).

   $$0 \times 5 = 0$$

   Step 2: Perform the subtractions from left to right.

   $$84 - 0 - 13 = 84 - 13 = \boxed{71}$$

10. Step 1: Perform the addition inside the parentheses.

    $$(20 + 25) = 45$$

    Step 2: Divide the result by 5.

    $$45 \div 5 = \boxed{9}$$

Classwork

1. Use commutative property to prove the following: The commutative property of addition states that for any two numbers $a$ and $b$, $a + b = b + a$.