National Mathematics Day 2019 (Source: Getty Images)

By Meenambika Menon

On National Mathematics Day 2019, here are some interesting facts about the subject that you can quiz your child about.

1. Among all shapes with the same perimeter a circle has the largest area. Among all shapes with the same area circle has the shortest perimeter.

2. 40 when written "forty" is the only number with letters in alphabetical order, while "one" is the only one with letters in reverse order. 'FOUR' is the only number in the English language that is spelt with the same number of letters as the number itself.

3. Multiplying ones always gives you palindromic numbers If you multiply 111,111,111 × 111,111,111 you get 12,345,678,987,654,321 - a palindrome number that reads the same forwards or backwards. And that works all the way back down to 11 x 11 (121) or just 1 x 1 (1).

4. Do you know the magic of no nine (9)? Multiply any number with nine (9) and then sum all individual digits of the result (product) to make it single digit, the sum of all these individual digits would always be nine (9).

5. If you add up the numbers 1-100 consecutively (1+2+3+4+5...) the total is 5050.

6. How do you add 1 to 100 quickly

1 +2 +3 +4……………………………+97+98+99+100

100+99+98+96…………………………… +4 +3 +2 + 1

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101 + 101………………………………………………………..101

101x100 = 10100

So the sum is 101200/2 = 5050

7. A 'jiffy' is an actual unit of time for 1/100th of a second.

**Also Read| Not good at mathematics? Your child can still be a whiz at it**

8. Have you heard about Fibonacci? It is the sequence of numbers wherein a number is the result of adding the two numbers before it! Here is an example: 1, 1, 2, 3, 5, 8, 13, 21, 34, and so on.

9. This is seen in the arrangement of petals in many flowers, arrangement of seeds in a sunflower plant, arrangement of cones in a pine cone, scales of pine apple etc. The spiral shapes of sunflowers and other patterns in nature follow a Fibonacci sequence.

8. Hexagon The geometry of this shape uses the least amount of material to hold the most weight,” Bees, masters of geometry, use hexagons to build their honeycombs.

9. If we take any three dimensional solid with flat faces known as polyhedron- for instance a cube, pyramid or a soccer ball, then adding the number of faces to number of vertices and then subsequently subtracting the no. of edges always give us the answer of 2. E.g. Cube possessing 6 faces, 8 vertices and 12 edges would come to 6+8-12= 2.

10. Among all the solid geometrical figures, triangle shapes are often used in construction because of their great strength.

11. You multiply Pi multiplied by the radius squared to find the area of a circle πr2 and multiply area by height to find the volume, that means the volume of a pizza that has a nominal radius of (z) and height (a) will be: Pi × z × z × a

And strangely, if you enter Pi to two decimal places (3.14) in your calculator and look at it in the mirror, you'll see it spells 'pie'.

12. In a crowded room, two people probably share a birthday It only takes 23 people to enter a room to give you an even chance that two of them have the same birthday. With 75 people in the room the chances rise to 99 per cent.

13. In a given list of numbers representing anything from populations to building heights to border lengths, fully one third of them will begin with the digit 1. Fewer will begin with 2 and so on until only one number in twenty begins with a 9. The bigger the data set, and the more orders of magnitude it spans, the more strongly this pattern emerges.

14. If you divide any number by 7, and the answer isn't an integer, you end up with the sequence 142857 recurring.

15. Take any four-digit number and multiply it by 73, then multiply the result by 137, your result is the four-digit number repeated twice.

16. The numbers on opposite sides of a dice always add up to seven On a dice the numbers 1,2 and 3 all share a vertex. If these three numbers run clockwise round this vertex then the dice is called left-handed and if the three numbers run anti-clockwise round the vertex, then it is a right-handed dice. Chinese dice are normally left-handed and Western dice are normally right-handed.

17. The number 0.999999….. is exactly equal to 1

Proof: Let x=0.9999…Then 10x = 9.9999…

10x-x =(9.9999…)-(0.9999…)

9x=9

x=1

18. If you shuffle a pack of cards properly, chances are that exact order has never been seen before in the whole history of the universe.

19. Zero is the only number that can't be represented in Roman numerals.

20. Major Indian contribution to present day Mathematics

- Place value system
- Introduction to ZERO
- Infinity - any number divided by zero is infinity

*(The author is lead, Curriculum – Science & Math at Shiv Nadar School)*