(2y +1)(4y + 1) is the factored form
N=54........................
Jill had a total score of 40 on 13 quizzes, so her average was
40/13 ≈ 3.08
_____
1 quiz @ 1 = total of 1
3 quizzes @ 2 = total of 6
4 quizzes @ 3 = total of 12
4 quizzes @ 4 = total of 16
1 quiz @ 5 = total of 5
total score = 1 + 6 + 12 + 16 + 5 = 40
total quizzes = 1 + 3 + 4 + 4 + 1 = 13
I = P x r x t
r = I/P x t
r = 310/1000 x 5
r = 0.62
r = 0.62 x 100
r = 62%
It follows from the definition of the binomial coefficient:
So we have
That is, 
gets absorbed into the numerator's factorial, and we introduct 
into the denominator. Now, 
, so we get
as required.
