Mental Math

Mental Addition Strategies

• Mental math is a skill that helps students to do math in their heads without using paper and pencil.
• Mental Math is useful in school and everyday life.
• It also helps to do calculations faster.
• Here, we will discuss the tricks and tips for addition.

Method 1:

• To add two or more numbers, split the second addend as per its place value.
• Then add the numbers.

Example :

Answer:

458 + 243

= 458 + 200 + 40 + 3 = 658 + 40 + 3 = 698 + 3 = 701

Method 2:

• To add two or more numbers, split both addends as per their place value.
• Then add the numbers.

Example :

Method 3:

• To add two or more numbers, first round off the numbers to their nearest hundreds or tens, and then add.
• After that add/subtract the deficiency of numbers from the result.

Example :

Answer:

a) 123 → 120

244 → 240

120 + 240 = 360

Add the deficiency.

3 + 4 = 7

360 + 7 = 367

b) 286 → 290

479 → 480

290 + 480 = 770

Then subtract the deficiency.

4 + 1 = 5

770 – 5 = 765

Method 4:

• This method is called ‘Number Thievery’
• To add the numbers, redistribute the numbers such that the numbers are easier to add.

Example :

Answer:

a) 141 + 426 =

Turn 141 to 140 and 426 to 427 by subtracting and adding 1 respectively.

Now, 140 + 427 = 567

Hence, 141 + 426 = 567

b) 589 + 356 =

Turn 589 to 590 and 356 to 355 by adding and subtracting 1 respectively.

Now, 590 + 355 = 945

Hence, 589 + 356 = 945.

Method 5:

• This method is called the benchmark method.
• Here, the numbers are splitted into two parts such that the addition of any part with the other addend results in any multiple of 10.
• This makes the addition easier.

Example :

Answer:

a) 518 + 5 = 518 + 2 + 3

= 520 + 3 = 523

b) 729 + 6 = 729 + 1 + 5

= 730 + 5 = 735