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NUMBER MAGIC

Believe it or not, numbers can be fun and intriguing.  The following examples of some number games are a good way to get children interested in arithmetic and these are just the tip of the iceberg.

Here are a few examples -

Sum of Human Knowledge (contributed by Eric Bishop)

If you multiply the number 142,857 by anything between 1 and 6 the answer contains the same digits.

e.g. 142857 x 3 = 428571      and       142857 x 6 = 857142

If you multiply the same figure by 7 the answer is 999,999.

Challenge 1

Add up the following numbers out loud, starting at the top and, adding on each number as you go -

 1000 40 1000 10 1000 40 1000 10

If you made the answer 5,000 (as 99% of people do) then try again!

Challenge 2

A game to find out a person's age and how many coins they are carrying.

• Ask someone to double their age (either mentally or on paper) but, obviously, they must not tell you.

• Then to add 5 and multiply by 50.

• Finally, they must add the number of coins they have on them.   If they do not have any, nothing is added.

• They then tell you the final answer.

• Now all you have to do is take away 250.  The first two digits of the answer you are left with are the persons age and the last two the number of coins in their possession.

This works unless they are carrying over 100 loose coins.

Example -   25 x 2 = 50 + 5 = 55 x 50 = 2750 + 6 = 2756

2756 - 250 = 2506

Challenge 3

Take any three digit number in which the first and last number differ by more than one i.e. 335 would be O.K. but not 333, or 332.

Reverse this number

Subtract the smaller number from the larger.

Example 1:-

335    Reversed = 533

533 - 335 = 198

198 + 891(198 reversed) = 1089

Example 2:

932 reversed = 239

932 - 239 = 693

693 +396 = 1089

Challenge 4

Get a friend to throw a dice three times and you will be able to tell them which numbers came up and in which order.

This is what they have to do -

• Throw dice

• Multiply number by 2

• Multiply by 5 (Remember this total)

• Throw dice second time

• Add this second number to the previous total.

• Multiply by 10 (Remember total)

• Throw the dice for the third time and add the number to the last total.

Ask for the final total.  Subtract 250 and you will be left with three figures.  These figures represent the numbers thrown and the in which they appeared.

Example:

First throw = 4

4 x 2 = 8

8 + 5 = 13

13 x 5 = 65

Second throw = 2

65 + 2 = 67

67 x 10 = 670

Third throw = 6

670 + 6 = 676

676 - 250 = 426 = 4 2 6