Its flawed as a "proof", but it might contextually justify the answer. That exact reasoning accounts for pretty much all of my limited success at middle school

Its flawed as a "proof", but it might contextually justify the answer. That exact reasoning accounts for pretty much all of my limited success at middle school/high school math competitions. You can usually skip long, difficult steps by simply assuming there is a single constant answer (as the rules of the contests usually make clear must be the case).