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barn32
04-09-2013, 03:05 PM
On this page (http://math.stackexchange.com/questions/37167/combination-of-smartphones-pattern-password) is a photo of a cell phone lock screen and some dialogue about how to figure out the number of combinations.

With my phone you need a minimum of four, sequential, non repeating dots to unlock your phone.

How many combinations are there for doing that with exactly four dots, and how do you figure it out?

At the bottom of the page someone "brute forced" the answers and came up with 1624. He starts with one then two, three etc.

The total number of combinations using four to nine dots is 389,112.

I'm having trouble figuring out how he came up with the number of combinations for just connecting two dots. He has 56, and I came up with 40.

It must be something simple, but I don't have the time to try and figure it out.

What am I missing?

therussmeister
04-09-2013, 05:37 PM
The number of possible combinations using 4 dots is exactly like the number of superfectas combos in a 9 horse race. The formula is 9*8*7*6= 3,024

The number of 2 dot combos are 9*8=72 just like the number of exacta combos in a 9 horse race.

barn32
04-09-2013, 05:46 PM
The number of possible combinations using 4 dots is exactly like the number of superfectas combos in a 9 horse race. The formula is 9*8*7*6= 3,024

The number of 2 dot combos are 9*8=72 just like the number of exacta combos in a 9 horse race.OK, but is that only true if you can use every possible combination? With these lock codes the dots have to be sequential.

In other words, (think of a telephone keypad) you can't go from one to nine or vise versa. If you start with 1, the next dot has to be 4,5, or 2, which eliminates 3,6,7,8 and 9.

therussmeister
04-09-2013, 06:01 PM
Yes, I realized that shortly after I posted, but it is not quite as limited as you think. If you start at 1, you can choose 2,4,5,6,8 next, only spots you cannot choose next are the other three corners.

barn32
04-09-2013, 06:07 PM
Yes, I realized that shortly after I posted, but it is not quite as limited as you think. If you start at 1, you can choose 2,4,5,6,8 next, only spots you cannot choose next are the other three corners.OK, thanks I didn't know that.

Longshot6977
04-09-2013, 06:24 PM
Yes, I realized that shortly after I posted, but it is not quite as limited as you think. If you start at 1, you can choose 2,4,5,6,8 next, only spots you cannot choose next are the other three corners.

Actually, if you start at 1, you can only choose the next adjacent keys which would be only 2,4 or 5. Watch the video to see the allowable sequence.

therussmeister
04-10-2013, 01:30 PM
Actually, if you start at 1, you can only choose the next adjacent keys which would be only 2,4 or 5. Watch the video to see the allowable sequence.
I use such a program, (although it may be from a different company with different rules), and I assure you, you can choose all except the corners, but it is difficult to "thread the needle" without accidentally hitting another spot unless you literally think outside the box.

DJofSD
04-10-2013, 03:14 PM
The problem is not sufficently defined.

If some one has a phone with the security feature like what is in the video, tell me if you can connect these two dots: 1 & 9. I would attempt to connect those two dots by not drawing the line through 5 but around it.

therussmeister
04-10-2013, 05:30 PM
You cannot connect 1 & 9 (unless 5 has already been used), nor can you connect 1 with 3 or 7

_______
04-10-2013, 07:11 PM
I understand this was posted here just as an intellectual puzzle. But can someone explain to me why anyone would come up with a security feature that acted to reduce the possible combinations available to open the phone?

A simple 4 digit lock has 10,000 solutions. The same 4 digit dot pattern has something less. I think the real intellectual challange is figuring out what would inspire someone concerned about security to choose this less secure option.

Greyfox
04-10-2013, 07:33 PM
I understand this was posted here just as an intellectual puzzle. But can someone explain to me why anyone would come up with a security feature that acted to reduce the possible combinations available to open the phone?

A simple 4 digit lock has 10,000 solutions. The same 4 digit dot pattern has something less. I think the real intellectual challange is figuring out what would inspire someone concerned about security to choose this less secure option.

Good question. But an other intellectual challenge is "Who be you?"__________

therussmeister
04-10-2013, 07:35 PM
I think some people would rather remember a pattern than a string of digits.

barn32
04-10-2013, 09:24 PM
Well I tried this pattern on my phone (1-8-3-4) and it worked.

Initially, I was just curious about how many combinations there were, and how you determined the number of combinations mathematically.

But sadly, after doing a little digging, I found it is very easy to get into any phone that is locked in this way.

JustRalph
04-10-2013, 10:12 PM
If it is IOS you can use Siri to get in without any fancy tricks

_______
04-11-2013, 01:12 AM
Good question. But an other intellectual challenge is "Who be you?"__________

I'm _______ but it's pronounced ______. The second _ is silent.

Greyfox
04-11-2013, 01:52 AM
I'm _______ but it's pronounced ______. The second _ is silent.

This is like the old quiz show "What's My Name?"

Are you in the Witness Protection Program or Jay Carney? :lol:

Red Knave
04-11-2013, 09:30 AM
I'm _______ but it's pronounced ______. The second _ is silent.
I was drinking coffee when I read that.
Now I have to change my shirt!

:)