In this wonderful Math trick we will write any three digit number twice, then we will divide it by 7, 11 and 13 and surprisingly we will get the same number back. You can try this out with your friends and surprise them. Let’s see how it’s done. Suppose your friend writes down 245. We will write another 245 to make the number 245245. Now we will first divide this number by 7, then by 11 and finally by 13. 7, 11 and 13 are consecutive Prime Numbers. On dividing 245245 by 7 we get a remainder of 35035. Now we’ll divide 35035 by 11. On doing we will get a remainder of 3185. Finally, divide 3185 by 13 and we get a remainder of 245 – exactly the SAME NUMBER from which we started.
Why did this happen? First we wrote the number 245, and then wrote it again by the side to get the six digit number 245245. However, when we multiply 245 by 1001 we will get 245245.
Well 245 x 1000 = 245000. On adding 245 to it we will get 245000 + 245 = 245245.
We also see that on multiplying 7 x 11 x 13 we will get 1001
This means multiplying a number by 1001 will the same as multiplying it by 7, 11 and 13 and the number will repeat itself. For instance 245 when multiplied by 1001 will become 245245.

This work is supported by IUCAA (www.iucaa.in) and TATA Trust (www.tata.com/aboutus/sub_index/Tata-trusts)

Credits:,Ashok Rupner, Manish Jain, Pradnya Pujari, Shivaji Mane, Jyoti Hiremath, Arvind Gupta, Vidula Mhaiskar

Dubbed in Kannada by PK Nanawaty TATA Trust: Education is one of the key focus areas for Tata Trusts, aiming towards enabling access of quality education to the underprivileged population in India. To facilitate quality in teaching and learning of Science education through workshops, capacity building and resource creation, Tata Trusts have been supporting Muktangan Vigyan Shodhika (MVS), IUCAA's Children’s Science Centre, since inception. To know more about other initiatives of Tata Trusts, please visit www.tatatrusts.org

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