Rosalee is inviding 5 friends to a party and each friend will get 4 cookies how many cookies does rosalee nee to get

Rosalee is inviting 5 friends to a party. Each friend will acquire 4 cookies.
So, let's count from 1-5 and give each friend 4 cookies.

1(4) + 1(4) + 1(4) + 1(4) + 1(4)
4 + 4 + 4 + 4 + 4
8 + 4 + 4 + 4
12 + 4 + 4
16 + 4
20.

Rosalee will require 20 cookies in total.

I hope this helps!

He needs to get 20 cookies 5 friends and 4 cookies each (5 X 4 = 20)

No a triangle cannot be formed because when you add the two smallest number together (which would be 11) the have to be bigger than the number it is "against" ( which would be 12)