https://www.gregmat.com/quizzes/quiz/im-overwhelmed-arithmetic-progress-quiz-2 (Question 8)
in his correction he says (14-2)/2+1=7 for the multiples of 2 but isn’t there 11 multiples of 2 ?
if i do it by hand i can find that 15! is divisible by 2^11
He isn’t exactly wrong but his wording makes the understanding of the correction difficult