Practice the questions given in the worksheet
on mental math addition and subtraction. There are some tricky mental arithmetic skills, you can use to to solve the questions of addition and subtraction easily and conveniently.
Something mentally interesting in addition and subtraction:
1. There is a square 3 × 3 division. The numbers from 1 to 8 are filled in the divisions in such a way that the sum of the three numbers in each line (vertically, horizontally and diagonally) is 15. This square is called Magic Square of numbers 1 to 8 with sum 15.
1 – 8, to make a sum of 15
Complete the four magic squares by filling the proper numbers in the blanks and some other magic squares may also be formed:
(v) 6 – 14, to make a sum of 30
(vi) 7 – 15, to make a sum of 33
(vii) 8 – 16, to make a sum of 36
(viii) 9 – 17, to make a sum of 39
2. There is a triangle having three sides equal. Six numbers are placed at its corners and at the middle of each side separately. The sum of three numbers of each side is the same. Such a triangle is called magic triangle.
To make a sum of 18
Complete the following magic triangle to place the proper numbers at the proper places:
To make a sum of 21 To make a sum of 18
3. Read the following sentences. The result of each is same.
(i) Taking out 3 from 5, how much will be left?
(ii) What will be the result after subtracting 3 from 5?
(iii) What should be added to 3 to get 5?
(iv) What is the difference between 5 and 3? The result is the same.
Is the result same for the following questions? If yes, then what is the result?
(i) Deduct 16 from 29,how much is left?
(ii) Subtract 26 from 39, find the result
(iii) What should be added to 17 to get 30?
(iv) What is the difference between 43 and 30?
4. (i) The sum of two numbers is 99, if one number is 45, find the other one.
(ii) There were 65 men in a bus. 15 of them got down at a bus-stop. How many men are now in the bus?
(iii) Out of 45 students of a class 7 students failed. How many students passed?
5. On a square field, there are three open rooms at its four sides. Three cows are placed in each side-room. In each side of the square there are 9 cows in count. But the total number of cows is 24.
Four more cows come. Arrangement of putting the cows is so changed that the number of cows in each side of the square field remains the same, i.e., 9 cows as shown. But the total number of cows become 24 + 4 = 28
The next day eight out of 28 cows are removed and arrangement is re-changed in such a that the number of cows in each side remains the same, i.e. 9 and total number of cows now become 20.
Distribute Rs. 40 along the four sides of a square at three-points of each side such that the total sum of rupees may become 15 on each side. When Rs. 4 is taken out, the distribution along each side remains 15 and again if Rs. 4 more is taken out the distribution along each side remains the same Rs. 15.
Answers for the worksheet on mental math addition and subtraction are given below to check whether you get the exact answers when you use the tricky strategies to add and subtract mentally.
Answers:
1.
2.
3. (i) 13
(ii) 13
(iii) 13
(iv) 13
4. (i) 54
(ii) 50
(iii) 38
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