3rd Maths : Term 3 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+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
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) 543 + 210
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) 298 + 501
Step 1:
298 = 200 + 90 + 8
501 = 500 + 1
Step 2:
200 + 500 = 700
Step 3:
700 + 90 = 790
Step 4:
790 + 8 = 798
798 + 1 = 799
Answer: 799
(iii) 798 + 654
Step 1:
798 = 700 + 90 + 8
654 = 600 + 50 + 4
Step 2:
700 + 600 = 1300
Step 3:
1300 + 90 = 1390
1390 + 50 = 1440
Step 4:
1440 + 8 = 1448
1448 + 4 = 1452
Answer: 1452
(iv) 348 + 681
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) 543 + 218
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
(vi) 716 + 540
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