Page 147 - NUMINO TG_4A

Math Story Kaprekar Number
jOb ective Learn about Kaprekar numbers.

1. Textbook Instructions Math Story Kaprekar Number

Read the story to introduce the Kaprekar There was a milepost 3,025 along the railroad in India.
Number to the students. One day, a heavy storm came. The milepost fell over and split into two.
A mathematician named Kaprekar was passing by the railroad and saw
The Kaprekar Number is named after a the broken milepost. There, he discovered something about the number,
mathematician. This story is a true story of 3,025.
how he discovered the relationship between
two numbers. Hey!
If I add up the digits that are split

into two, 30 and 25, I get 55.
30 25 = 55

And the product of 55 and 55 is 3,025.
55 55 = 3,025

The numbers amazingly
go back to the original number.

3,0 25

80

2. Build Understanding

Kaprekar Number
A Kaprekar Number is a number, ABCD, where the sum of the two numbers it splits into two parts, AB and CD, is
squared to get the original number. The following equation shows this relationship.

ABCD (AB CD)2
There is only one 2-digit number and three 4-digit number that are Kaprekar Numbers.
2 digit Kaprekar Numbers: 81 (8 1 9 9 9 81)
4 digit Kaprekar Numbers: 9,801, 2,025, 3,025

130 NUMINO Teacher s Guide