Grade 3 Mental Math: Using Properties

Worked examples

Real problems from the practice worksheets, solved one step at a time.

1. Example 1

   4 × 4 × 5 = ?

   1. Look for friendly numbers: 4 × 5 = 20, a round number. Do that pair first, so now you have 4 × 20.
   2. Multiply: 4 × 20 = 80.
   3. So 4 × 4 × 5 = 80.

   Answer: 80

2. Example 2

   6 + 43 + 4 = ?

   1. Look for friendly numbers: 6 and 4 make a round number. Change the order to put them together: 6 + 4 + 43.
   2. Add: 6 + 4 = 10, so now you have 10 + 43.
   3. Add: 10 + 43 = 53.
   4. So 6 + 43 + 4 = 53.

   Answer: 53

3. Example 3

   2 + 46 + 8 = ?

   1. Look for friendly numbers: 2 and 8 make a round number. Change the order to put them together: 2 + 8 + 46.
   2. Add: 2 + 8 = 10, so now you have 10 + 46.
   3. Add: 10 + 46 = 56.
   4. So 2 + 46 + 8 = 56.

   Answer: 56