Home Community Write Blog 3 Digit - Math Tricks

User's Blog

A short description about your blog

Sep 14
2008

3 Digit - Math Tricks

Posted by: Bruce

Tagged in: Math Magic

Bruce

For this piece of magic you need a pretty clever audiences who is good at taking away (or can use a calculator).

Ask them to work this sum out:

  1. Write down a three digit number where all the digits are different.
    eg 317
  2. Reverse the digits eg 713
  3. Take the smaller number from the larger number
    713
    317
    -----  -
    396
  4. Ask them to tell you the hundreds digit or the units digit and you will be able to tell them the whole answer without knowing what numbers they chose!


THE SECRET:

The answer always has a 9 in the tens column. The hundreds digit and units digit always adds up to 9.

So, if the clever spectators says the hundreds digit is 3 you can work out that the units must be 9-3=6.

So the number must be 396.

If the clever parent says the hundreds digit is 5 that means the units will be 9-5=4 and the whole number will be 594 etc etc

Try it out for yourself, but make sure your spectators gets the subtraction correct!


Comments (8)

Another way!
0
Hey! If you name the hundred digit a, the ten digit b and the unit digit c than you can also just compute the result like:
(a-c)*100-(a-c).

So here for instance the number is 317 that means a=3, b=1 and c=7. So a-c=-4 and the result is
-4*100-(-4)=-396. Just remove the minus if you get something less than zero.

I find this easier to do. Try it yourself!
Hans252 , July 22, 2013
Another way!
0
Hey! If you name the hundred digit a, the ten digit b and the unit digit c than you can also just compute the result like:
(a-c)*100-(a-c).

So here for instance the number is 317 that means a=3, b=1 and c=7. So a-c=-4 and the result is
-4*100-(-4)=-396. Just remove the minus if you get something less than zero.

I find this easier to do. Try it yourself!
Hans252 , July 22, 2013
...
0
smilies/angry.gif i hate this trick
None of your beeswax , April 13, 2013
I asked my friend to do it....
0
She said
-1
.
None of your beeswax , April 13, 2013
...
0
IF 0 is in the hundredths place what we do to tell the answer
Manav , March 13, 2013
Excellent
0
This is great. Send me a few more.
Yathiraj , April 20, 2011
...
0
AWESOME i can't figure a way to prove you rong
opp , February 17, 2011
ytrytryrtyt
0
smilies/cool.gifsmilies/cool.gifsmilies/cool.gifsmilies/grin.gifsmilies/grin.gifsmilies/grin.gif
opp , February 17, 2011

Write comment

smaller | bigger
security image
Write the displayed characters

busy