Mental Addition & Subtraction by using Place value
a)Fast & Easy Addition
Doing addition & subtraction is not a difficult task, but by using conventional method it is difficult to do addition orally. Here we learn to add the number by adding their place value. By using place value one can easily add the numbers mentally.
First, we will solve by conventional method
Ex. i) 256 + 477
Step 1: In conventional method, first, we add from right hand side, 6+7 =13
3 retained as right most digit of the answer & 1 carry over to the left hand
Digit.
Step 2: Now we add, 5 +7 = 12+ 1 (Carry)= 13, Here 3 retained in answer & carryover 1 to the leftmost digit.
Step 3: Now add 2 + 4 = 6 + 1 (Carry) = 7
Answer = 256
Now, if we try to add this number mentally then it’s not possible by conventional method, for mental addition we must add them by their place value.
256 + 477 is,
200 + 400 =600 (Add place value of first digit)
50 + 70 = 120 (Add place value of second digit)
6 + 7 = 13 (Add place value of third digit)
Now add the results, 600 + 120 + 13 = 733.
Answer, 256 + 477 = 733
OR
256 + 477
Take 256 & add 400 (Place value of first digit)
256 + 400 = 656
Now, add 70 (Place value of second digit)
656 + 70 =726
Now add 7 (Third digit place value)
726 + 7 =733
Answer, 256 + 477 = 733
Ex. ii) 4567 + 2543 + 7896
4000 + 2000 + 7000 =13000
500 + 500 + 800 = 1800
60 + 40 + 90 = 190
7 + 3 + 6 =16
Add the results,
13000 + 1800 + 190 + 16 =15006
Answer, 4567 + 2543 + 7896 = 15006
Ex. iii) 456 + 762
456 + 700 =1156
1156 + 60 =1216
1216 + 2 = 1218
Answer, 456 + 762 = 1218
Ex. iv) 7206 + 2366
7976 + 2000 = 9206
9206 + 300 = 9506
9406 + 60 = 9466
9466 + 6 =9472
Answer, 7206 + 2366 = 9472
b) Easy & Fast Subtraction:
Ex. v) 4288 – 3219
First, we will solve by conventional method,
Step 1: we start to subtract number from RHS.
8-9, Here we need to barrow from left hand side digit
So, we borrow 1 from 7
Now, 18 -9 = 9
Step 2: Now we subtract 10th place number,
6 -1 = 5 (Here we subtract from 6, as we borrow 1 from 7)
Step 3: Now we subtract 100th place number
2-2 = 0
Step 4: Now we subtract our right most digit,
4 – 3 =1
So, our answer is, 1059
But by using conventional method it is not possible to subtract number mentally, so for mental subtraction we will use place value of the number.
Now we will solve by using place value,
4278 – 3219
4278 – 3000 =1278 (Subtract place value of 1st number from right)
1278- 200 = 1078 (Subtract place value of 2nd number)
1078- 10 = 1068 (Subtract place value of 3rd number)
1068 – 9 = 1059 (Subtract place value of 4th number)
So, Answer = 1059
By practicing we can do subtraction orally.
Ex. vi) 567 – 348
567 – 300 =267
267 – 40 =227
227 – 8 = 219
Answer, 567 – 348 = 219
Ex. vii) 4356 -1478
4356 – 1000 =3356
3356 – 400 = 2956
2956 – 70 = 2886
2886 – 8 = 2878
Answer, 4356 -1478 = 2878
Try This Orally:
i) 453 + 673 ii) 2351 + 5322 iii) 1546 + 243
iv) 345-267 v) 5672 – 4378 vi) 3412 – 2423
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