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# (Resolved) Maths genius required: nCr function

Bit of long shot, but maybe I might get a maths genius reading this.

I'm having a bit of trouble with the nCr function to calculate the max number of permutations under specific circumstances. I can work everything out fine when only having two variable factors but when I add a third my maths seems to go wrong

Basically I have a maximum distribution of 94^7 in a string value. This means 94 characters are possible, in a string of length 7.

I then am trying to break this up based on different patterns

e.g. from this string of 7 characters, 1 is a number (10 different choices), 1 is a special character (58 choices) and the remainder are alphabetic (26 different choices)

I am currently working this out like this: P(5a + 1n + 1s) = ( (7 nCr 1) * 10) * ( (7 nCr 1) * 58) ) * (26^5).

The problem is after working out all the possible permutation distribution areas - I am never hitting the maximum distribution when toting them up. I've got a feeling it's got something to do with the way I am working out the distribution areas above, but I can't seem to find the problem.

Mucho thanks for anyone who can help me solve this problem.

I'm having a bit of trouble with the nCr function to calculate the max number of permutations under specific circumstances. I can work everything out fine when only having two variable factors but when I add a third my maths seems to go wrong

Basically I have a maximum distribution of 94^7 in a string value. This means 94 characters are possible, in a string of length 7.

I then am trying to break this up based on different patterns

e.g. from this string of 7 characters, 1 is a number (10 different choices), 1 is a special character (58 choices) and the remainder are alphabetic (26 different choices)

I am currently working this out like this: P(5a + 1n + 1s) = ( (7 nCr 1) * 10) * ( (7 nCr 1) * 58) ) * (26^5).

The problem is after working out all the possible permutation distribution areas - I am never hitting the maximum distribution when toting them up. I've got a feeling it's got something to do with the way I am working out the distribution areas above, but I can't seem to find the problem.

Mucho thanks for anyone who can help me solve this problem.

Original Poster

Studies (not homework though lol)

Original Poster

The way I understand it is that nCr gives you the number of combinations possible for a given distribution. So for the situation of two numbers in any position, out of a total of 7 possible positions = 7C2 = 21.

I think I misread the question - it's a long time ago since I did maths! Sorry, I don't think I can help!

All I remember of nCr is that 10C3 means there could be 10 balls in a hat, and 10C3 would be the number of different combinations that 3 balls could be taken out! At the moment I can't see how to relate this to your problem

I'm sure someone will be along to help though!

Good luck.

Original Poster

Thanks for that.

I just found out I've been messing up the formula all along - a true doh moment lol.