# choosing from numbers whose sum is X

Asked by Matlabbey on 11 Sep 2012
Latest activity Commented on by Matlabbey on 11 Sep 2012

hi all,

suppose i generate 1000 random numbers and want to pick five out of that 1000 so that the sum of the five numbers is 100. if there is no way so the sum equal to 100 then i will just re run it. it doesnt have to work always...thank you!!

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Answer by Matt Fig on 11 Sep 2012
Edited by Matt Fig on 11 Sep 2012

I suppose you mean integers, but you don't say....

```N = round(randn(1,1000));
S = 0;
maxiter = 2e6;
cnt = 1;
```
```while S~=5 & cnt<maxiter
R = ceil(rand(1,5)*1000);
S = sum(N(R));
cnt = cnt + 1;
end
```

Now we have the numbers, so look at them:

```nums = N(R)
sum(nums)
```

Matlabbey on 11 Sep 2012

hi, thank you yes i do mean integers. but this doesnt seem to have a fixed sum?

Matt Fig on 11 Sep 2012

What do you mean, no fixed sum? I generated 100 random numbers and chose 5 whos sum is 5. If you need to change it to the sum being 100, then just use:

```while S~=100
```

You might also like a different distribution. So:

```N = round(randn(1,1000)*20);
N = randi(100,1,1000); % etc...
```
Matlabbey on 11 Sep 2012

sorry, you're right!! thank you!!

Answer by Sean de Wolski on 11 Sep 2012
Edited by Sean de Wolski on 11 Sep 2012