## Short Math Brain Teaser, 2 Digit Number

Now that summer is drawing to a close, and many folks are returning home from their vacations, the rate of new updates and posts here will start to return to usual levels. Besides, at least where I live, it’s almost too hot to do anything fun outdoors!

Have accumulated a number of really good challenges that our regulars have sent in, and now that school is starting up again, will start to unleash some of them :

Here’s 1 of 3 that Suineg sent ( a relatively easy one first!):

What 2 digit number is the same as the double of the product of its two digits?

*Related:*

Math Brain Teasers and Puzzles from the Smart-Kit archive

Bobo The Bear| PUZZLE MASTER | Profile August 17th, 2010 - 1:00 am36 = 2x(3×6)

munna| Profile August 17th, 2010 - 1:44 amThe two digit number is 36.

2 * (3 * 6) = 36

Hex| PUZZLE MASTER | Profile August 17th, 2010 - 4:14 am36

Shawn| PUZZLE GRANDMASTER | Profile August 17th, 2010 - 8:40 am36

John Lewis Highsmith| Profile August 17th, 2010 - 9:07 am36

Hendy| Profile August 17th, 2010 - 3:18 pm36

Hendy| Profile August 17th, 2010 - 3:52 pmIf you consider “00” a two digit number it also applies to the question.

Hex| PUZZLE MASTER | Profile August 18th, 2010 - 7:48 amAway from the serious talk, 00 cannot be a 2 digit number because:

1- 00 would be a 6 digit number (following the same logic)

2- RK would owe me a 6 digits figure (00)

suineg| PUZZLE MASTER | Profile August 19th, 2010 - 12:24 pmNice, 36 is the answer I had in mind, because 00 is 0 so 1 digit… maybe not, in a clock, ok cool.

Explanation:

AB= 2AxB from this B has to be even

A0+ B= 2AxB

A0= (2xA-1)xB

so this mean 2xA-1 has to be 5 or 15 for A0 to be possible

but with 15, A=8 and 80 is not a multiply of 15 so:

2xA-1 = 5

A= 3

30= 5xB

B= 6

the number is 36, cool!!!

BlindCupid| Profile August 20th, 2010 - 9:31 am36

Hendy| Profile August 25th, 2010 - 7:01 pm0 is a one digit number

00 is a two digit number

000000 is a six digit number

When speaking in computer terms, my world of work, it makes a huge difference. Every bit, byte, and character makes a difference.

A sign character is neither a digit nor a number so I was at least able to rule out negative numbers. However, I went to the extra trouble of ruling out hexadecimal numbers. Only ’00’ and ’36’ still apply. I did not look at octal, but that could be next. Binary definitely does not work, since the complete set of two digit numbers is ’00’, ’01’, ’10’, and ’11’.

As you can see terms like “number” and “digit” are very loaded terms in certain circles. Had you said digits in the decimal system with units being the inclusive set of 0-9, then you have appropriately bounded the problem as far as number system. Then you have to claim that ’00’ is not a two digit number in the decimal system. Then nitpickers and detail minded people like me cannot find loopholes. For puzzles, it doesn’t really matter so much. For rockets and space related mathematics, things go boom when we are imprecise.

Yehuda Groden| Profile September 15th, 2010 - 4:11 pm36 = 2(3*6)

Ogidi| Profile September 16th, 2013 - 5:13 am36