Videos Test Yourself Books MathFacts Math Diagnostics Math Tricks Daily PhysEd
Class Photos Worksheets Insectclopedia Musiclopedia Techlopedia Teacher Timesavers Study Guides
Calendars and Hundred Squares
Thanks S Froggatt

monthly calendar.

Effect :
Find a  page from a calendar.
Ask a participant to circle a square of 9 dates.

Here is an example:





1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31


Now ask the participant to reveal the total of the smallest and the largest numbers.
The participant says 26. Immediately call out all nine dates in his square.

Ask another participant to choose a different set of nine dates. 
This time ask the participant for the centre date in her square. 
Immediately tell her the total of all the dates she selected! 

Next task : the hundred square
Ask each pupil to choose a 4 x 4 square of numbers.
Ask them to call out the total of their smallest and biggest.
Respond by telling them their first row.

How can you do this?

Method
Do mental algebra to start off. 
If I am thinking of a number d, what is the number after mine? 
Answerd + 1. 

We draw three grids, one for each trick:

d

d + 1

d

2d + 16. Just divide by 2 and subtract 8 to get the first number, then count on.

+ 2

d + 7

d + 8

d + 9

d + 14

d + 15

d + 16

d - 8

d -7

d

The total is just 9d since all those + and – numbers cancel out. IJust multiply the number by 9.

- 6

d -1

d

d + 1

d + 6

d + 7

d + 8

d

d + 1

d + 2

d

Subtract 30, then 3, from 2d + 33, then halve the result. Once you know the first number, the first row is easy.

+ 3

d + 10

d + 11

d + 12

d + 13

d + 20

d + 21

d + 22

d + 23

d + 30

d + 31

d + 32

d + 33