KCG Interview Question: How do you check if your regr... | Glassdoor.co.uk

## Interview Question

Quant Trader Interview London, England

# How do you check if your regression parameters are

significant? Given a number's prime number decomposition, how many ways are there of factorizing it into two different factors?

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answer to prime number question: I am assuming that the 2 factors you factorize it into are relatively prime, in that they have no common factors. For a number N, suppose it is represented as a product of prime number N=\Pi_i p_i^(e_i), where p_i is a prime number and e_i represents the number of such primes in N's prime number factorization. For N=xy, we see that for each p_i, we can choose whether ALL p_i factors go to x or go to y (2 choices). it cannot be that we take some of the p_i factors and give them to x, then give the others to y because otherwise x and y will have common factors. Thus, for each p_i we have 2 choices as to where it can go: x or y. So nominally we have 2^n possibilities. However, since (a)(b) and (b)(a) are considered the same factorization, we over count by a factor of 2, so really we have 2^(n-1) possibilities.

fermi on 13 Oct 2015
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regarding my above answer: the upper limit on the product \Pi should be n. That is, \Pi_{i=1}^n

fermi on 13 Oct 2015
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your assumption of relatively prime makes the problem easy...i don't think that's the goal...try to answer the actual question without making sweeping assumptions!!

Anonymous on 8 Feb 2017