Play with numbers

Think of a two digit number, say 42, then subtract the reverse of its digits, 24, from 42

42-24 =18

hence 18 is product of 9 

also 1+8=9

Choose any two digits number and for each one reverse the digits and subtract the smaller number from the larger.  Look at all the answers you get.  Do they all have a common divisor?  What do the digits sum to each time?  

Some Examples:

92-29 =63

hence 63 is product of 9 

also 6+3=9

41-14 =27

hence 27 is product of 9

also 2+7 =9

83-38 =45

hence 45 is product of 9

also 4+5 =9

You see how fascinating and enjoying it is. In each case the difference is divisible by 9 (i.e. the common factor is 9) and the sum of the digits of the difference is always 9.

Play with Numbers 

STEP 1
Ask a friend to write down a number (any number with more than 3 digits will do, but to save time and effort you might suggest a maximum of 8 digits).
Example: 83 972 105
STEP 2
Ask them to add the digits.
Example: 8+3+9+7+2+1+0+5 = 35
STEP 3
Ask them to subtract this number from the original one.
Example: 83 972 105 – 35 = 83 972 070
STEP 4
Ask them to select any digit from this new number and strike it out, without showing you.
Example: 83 972 070
STEP 5
Ask them to add the remaining digits and write down the answer they get.
Example: 8+3+9+7+0+7+0 = 34
STEP 6
Ask them to tell you the number they get (34) and you will tell them which number they struck out.

---

SOLUTION
The way you do this is to subtract the number they give you from the next multiple of 9. The answer you get is the number they struck out.
Example: The next multiple of 9 here is 36 (9 x 4 =36)
36 – 34 = 2 and there you have your answer, easy isn’t it!
Note: If the number they give you after step 5 is a multiple of 9, there are two possible answers then you simply tell them that this time they crossed out either a 9 or a zero.