Permutations formula

Thomk

New member
Hello community, I have this problem:
We've got a number range(min|max), say 10|100 . We randomly choose one. Say 70.
We have the ability to take pairs of numbers from within this range and make calculations with them. Operators used are +, -, *, /, % (Modulus Operator). We're trying to find how many permutations can give our selected result(70 in this case), taking into consideration the number of operators that can be used.
I think that this is in the correct subforum as it can be added into statistics/probabilities/combinations(?).
Anyway, I'm not the best at explaining maths in English, so here is my approach so far:
(((maxRange / target result) * (totalOperators * 9) * total numbers inside math calculation. Total numbers inside math calculation is this "pair" thing I said, so in this case it's 2(two numbers consist the combination). Target result is 70 in this case. Max range is max selected(100 here). Total operators is the operators we have available(5).
This seems to be giving some results but I'm not sure it's ok though. If anyone is able to understand anything of this mess, help would be appreciated. Thanks in advance.
Ps. Range of numbers will always be >=1. Range numbers, selected result and permulations are natural numbers .

Last edited:

Otis

Senior Member
… We're trying to find how many permutations can give our [randomly-selected number] (70 in this case) …
The following examples seem to be what you're calling 'permutations'.

80 - 10
81 - 11

99 - 29
100 - 30

10 + 60
11 + 59

59 + 11
60 + 10

7 × 10
10 × 7

Does order make a difference, in your counting?

Thomk

New member
Yep, order does make a difference. For instance 7x10 is different than 10x7