an urn contains 13 numbered balls, of which 7 are red and 6 are white. A sample of 5 balls is to be selected. How many samples contain at least four red balls?

Question

anonymous · Answer

this is going to be a royal pain

anonymous · Answer

whoa i should learn to read
you only are picking 5 balls right?

anonymous · Answer

how many ways to pick 4?

anonymous · Answer

i guess i am asking if you know the answer, if not i can show you

anonymous · Answer

well to pick four would just be 7C4 x 6C1 right? tbh idk

anonymous · Answer

pick five is $$\binom{7}{5}$$ pick four is $$\binom{7}{4}\times \binom{6}{1}$$

anonymous · Answer

yeah what you said, i just used different notation

anonymous · Answer

to pick four red balls right 
so would i just add 7C5 to 7C4 x6C1

ie 

7C5 + (7C4x6C1) ?

anonymous · Answer

yes

anonymous · Answer

and thats the answer, its that easy?