Well, if T is total time to build, D is the time that can be distributed equally among any number of workers, and C is constant, indivisible time extra time that goes along with construction, and X is the number of workers, then:
T - C = D / X
so, since T is 12 and 6 is half of 12, then:
T/2 - C = D/X * 1/2
or
T/2 - C = D/2X where X > 0, C = 0, T=12, and D = (T - C) / X
which is both the answer it's looking for (twice as many workers) and the correct answer (it depends on at least two things we don't know), while assuming what they're assuming, which is C = 0
(Stupid ass junior high math problems piss me off, junior high is a traumatic experience)
yup, but that answer was based entirely on the assumptions present in the question. D is all divisible work, and C is everything else, because that's literally all you can assume to make the math work. D has to therefore be 12 months worth of divisible work minus C. C could very well be 12 months of work, meaning D is zero and adding more workers won't matter.