Mathematics, Operations (+, -, x, /, etc.), Problem Solving

Grade 5- 8

### Objective

Students learn methods for easy mental multiplication.

### Directions

Tell students that it is possible to multiply large numbers in their heads using some simple techniques. Explain each technique to them and write the examples on the board as you go along.

Multiplying by 2 just means doubling the number.

Example: 340 x 2 = 680

Multiplying by 5 is done by multiplying by 10 and cutting the answer in half.

Example: 660 x 5 = ?

660 x 10 = 6,600

6,600 ÷ 2 = 3, 300

660 x 5 = 3, 300

Multiplying by 9 is done by multiplying by 10 and subtracting the other factor.

Example: 63 x 9 = ?

63 x 10 = 630

630 - 63 = 567

63 x 9 = 567

Multiplying by 50 is done by multiplying by 100 and dividing by 2.

Example: 34 x 50 = ?

34 x 100 = 3, 400

3,400 ÷ 2 = 1,700

34 x 50 = 1,700

Multiplying by 25 is done by multiplying by 100 and dividing by 4.

Example: 28 x 25 = ?

28 x 100 = 2800

2,800 ÷ 4 = 700

28 x 25 = 700

### Resources

- Easy Mental Multiplication activity sheet (one per student)
- pencils