Quick Ways of adding

UNIT −7

Information Processing

Quick Ways of adding

We perform addition of numbers in many situations daily. Let us learn some tricks which help us to add numbers quickly.

1. Using addition table is one of the good ways to add small numbers.

2. Let us know some facts in addition

i. Adding 0 to a number

 A number remains the same when you add 0 to it.

ii. Adding 1 to a number

When 1 is added to a number it gives the at number.

iii. Adding 2 to a number

When 2 is added to a number the numbers jumps or skips over 2 next to it.

iv. Adding 10 to a number

When 10 is added to a number its ones place remains the same and digit in 10 place is increased by 1 i.e., moves to the next number.

3. Finding the pairs of 10

When a set of numbers are given to add, We shall find the pairs of numbers gives the sum 10 and add them.

Example

Find the sum of 7+4+6+3

7+4+6+3

7+3=10 and 6+4=10

Hence the sum of the numbers =10+10=20

Example

Find the sum of 5+3+2+6+4

5+3+2+6+4

6+4=10 and 5+3+2=10

Hence the sum = 10+10=20

Exercise

Find the sum of

i) 5 + 1 + 5 + 9

ii) 2 + 5 + 5 + 7 + 1

iii) 3 + 6 + 1 + 2 + 8

i) 5 + 1 + 5 + 9

5 + 1 + 5 + 9

5+ 5 = 10 and 1+9=10

Hence the sum= 10+10=20

ii) 2 + 5 + 5 + 7 + 1

2 + 5 + 5 + 7 + 1

2+7+1=10 and 5+5=10

Hence the sum= 10+10=20

iii) 3 + 6 + 1 + 2 + 8

3 + 6 + 1 + 2 + 8

3+6+1=10 and 2+8=10

Hence the sum= 10+10=20

4. Doubling

i. We shall double a number when we add the same number twice.

Example

5 + 5 = 2 × 5 = 10

7 + 7 = 2 × 7 = 14

ii. We shall also use doubling when we add nearer numbers.

Example

5 + 6 = 2 × 5 + 1 = 10 + 1= 11

4+5 = 2 × 5 −1 = 10 −1 = 9

5. Adding two digit numbers

Add the ones and skip count the 10 s

Example

Find the sum of 7 + 12.

7 and 2 gives 9.

From 9 skip count in tens to get the sum 19.

7 + 2 = 9

9 + 10 = 19

Example

Find the sum of 25 + 33.

Adding ones 5 + 3 = 8

Skip counting 8 + 30 + 20 = 58

Example

Find the sum of 37 + 24.

Adding ones 7 + 4 = 11

Skip counting 11 + 30 + 20 =61

6) Adding three digit numbers

Example

Find the sum of 576 + 323.

Suppose, We need add the following numbers, We shall follow these steps to add them quickly.

Step : 1 − Expand the number 500 + 70 +6

 300 + 20 + 3.

Step : 2 − Add the hundreds 500 + 300 = 800

Step : 3 − Add the tens one by one 800 + 70 = 870

 870 + 20 = 890

Step : 4 – Add the ones by one 890 + 6 = 896

 896 + 3 = 899

Add the given big numbers using the above method.

 i)

 H T O

 5 4 3

+2 1 0

−−−−−−

−−−−−

Step 1 :

543 = 500 + 40 + 3

210 = 200 + 10

Step 2 :

500 + 200 = 700

Step : 3

700 + 40 = 740

740 + 10 = 750

Step : 4

750 + 3 = 753

Answer : 753

ii)

 H T O

 2 9 8

+5 0 1

−−−−−−

−−−−−−

Step 1 :

298 = 200 + 90 + 8 + 3

501 = 500 + 1

Step : 2

200 + 500 = 700

Step : 3

700 + 90 = 790

Step : 4

790 + 8 = 798

798 = 1 = 799

Answer : 799

iii) 

Step 1:

798 = 700 + 90 + 8

654 = 600 + 50 + 4

Step2:

700 + 600 = 1300

Step3:

1300 + 90 = 1390

1390 + 50 = 1440

Step4:

1440 + 8 = 1448

1448 + 4 = 1452

Ans: 1452

iv)

H T O

 3 4 8

+6 8 1

−−−−

−−−−

Step : 1

348 = 300 + 40 + 8

681 = 600 + 80 + 1

Step : 2

300 + 600 = 900

Step 3 :

900 + 40 = 940

940 + 80 = 1020

Step : 4

1020 + 8 = 1028

1028 + 1 = 1029

Answer : 1029

v)

 H T O

 5 4 3

+2 1 8

−−−−−

−−−−−

Step : 1

543 = 500 + 40 + 3

218 = 200 + 10 + 8

Step : 2

500 + 200 = 700

Step : 3

700 + 40 = 740

740 + 10 = 750

Step : 4

750 + 3 = 753

753 + 8 = 761

Answer : 761

v)

 H T O

 7 1 6

+5 4 0

−−−−−

−−−−−

Step : 1

716 = 700 + 10 + 6

540 = 500 + 40

Step 2 :

700 + 500 = 1200

Step : 3

1200 + 10 = 1210

1210 + 40 = 1250

Step : 4

1250 + 6 = 1256

Answer : 1256