Browse Teasers
Search Teasers

## For The Love of Calculators!

Probability puzzles require you to weigh all the possibilities and pick the most likely outcome.

 Puzzle ID: #45221 Fun: (2.62) Difficulty: (1.96) Category: Probability Submitted By: Fhqwhgads

Little Billy has a calculator with 15 buttons. He has 10 keys for 0-9, a key for addition, multiplication, division, and subtraction. Finally, he has an = sign. However, Mark the Meanie messed up the programming on Billy's calculator. Now, whenever Billy presses any of the number keys, it comes up with a random single-digit number. The same goes for the four operations keys (+,-,x, /). So whenever Billy tries to press the + button, the calculator chooses randomly between addition, multiplication, subtraction, and division. The only key left untouched was the = sign.

Now, if Billy were to press one number key, one operation key, then another number key, then the = button, what are the chances the answer comes out to 6?

There is a 4% chance.

There are 16 possible ways to get 6.

0+6
1+5
2+4
3+3
6+0
5+1
4+2
9-3
8-2
7-1
6-0
1x6
2x3
6x1
3x2
6/1

There are 400 possible button combinations.

When Billy presses any number key, there are 10 possibilities; when he presses any operation key, there are 4 possibilities.

10(1st#)x4(Operation)x10(2nd#)=400

16 working combinations/400 possible combinations= .04 or 4%

Hide

## What Next?

See another brain teaser just like this one...

Or, just get a random brain teaser

If you become a registered user you can vote on this brain teaser, keep track of
which ones you have seen, and even make your own.

 doodinthemood Sep 04, 2009 Quite a nice little puzzle, but anyone trained to think in the standard school maths puzzle solving way won't have many problems with it. dalfamnest Sep 04, 2009 I enjoyed it - quite simple with some basic probability understanding, but a good story to make it fun. Nicky101 Sep 05, 2009 Fun teaser! I forgot to switch around 6*1 and 6/1 completely slipped my mind . Matttoy Sep 08, 2009 I read the thing wrong i guess cuz I completely blanked. Then again I've only been up an hour and I'm tired! Stack1607 Oct 18, 2009 Great puzzle! But I didn't notice 6/1.. javaguru Dec 30, 2009 Nice clever puzzle. Very easy, but that's OK. Although I prefer the clever and diabolically difficult puzzles, clever easy puzzles are not that common. BriangleJJ Jul 08, 2010 Agreed... Messed up a little with the 6x1 and 1x6. Now does he have a ^2 function in his calculator??