need help with level D and E!!! http://www.insidemathematics.org/assets/problems-of-the-month/growing%20staircases.pdf

Question

anonymous · Answer

what's wrong with answer on previous question?

anonymous · Answer

i need the basic whole formula,so I can solve the questions on level D and E

anonymous · Answer

And you don't think formula is $\dfrac{n^2(n+1)}{2}$?

anonymous · Answer

you were already given formula in previous question by other user. use this formula for level D and E.

anonymous · Answer

what stopping you from doing that?

anonymous · Answer

that doesn't work

anonymous · Answer

that was for level A and B

anonymous · Answer

That's $\dfrac{n(n+1)}{2}$

Formula for D and E is same as A and B but multiplied by $n$.

anonymous · Answer

oh, but he told me n(n+1)/2

anonymous · Answer

thanks