Math Magic

Statistical problems involve multiple operations like multiplication, division and additions. A small mistake in these operations can lead to loss of 5 marks out of 6 in a single question, even though the steps and formulas used by the child are correct.  I have seen this happening multiple times when checking exam papers of high school children. Let’s see how we can prevent these mistakes by cross checking method.  It will help the child being confident and solve the exam paper calmly.

This is in continuation of the method discussed in my earlier article (i.e. checking accuracy of multiplication), the same method can be used to cross check addition, subtraction and division as well. Let’s see the method via the example shown below.

Checking the ACCURACY OF DIVISION

*We will follow the same methodology of dividing the sum of digits of a number by 9 and finding the remainder for all the steps below.

Let’s check a division problem

                                                     1481265 / 4281 = 346, remainder 39

Step 1 – Find the Remainder* from the Dividend 1481265, 1+4+8+1+2+6+5 = 27, Remainder* is 0

Step 2 – Find the Remainder* from the Divisor 4281,     4+2+8+1 = 15, Remainder* is 6

Step 3 – Find the Remainder* from the Quotient 346,     3+4+6 = 13, Remainder* is 4

Step 4 – Find the Remainder* from the Remainder 39,    3+9 = 12, Remainder* is 3

Step 5 — Multiply Remainders* in Step 2 & Step 3 and add remainder* of Step 4,

6 x 4 = 24, 24 + 3 = 27

Step 6 — Find Remainder* of the result in step 5, i.e. 27/9, Remainder* is 0

Remainder in Step 1 = Remainder in Step 6, shows the correctness of the division. This happens because (Divisor x Quotient) + Remainder = Dividend.

Now try using this method for addition and subtraction problems as well!

Kiran Bala Dash,

Grandparent of Tanay Sahu (4 E) and Vinay Sahu (LKG D)

Retired Lecturer in Maths, Directorate of Education, New Delhi