Question

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?

Answer 1

this is going to be a royal pain

Answer 2

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

Answer 3

how many ways to pick 4?

Answer 4

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

Answer 5

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

Answer 6

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

Answer 7

yeah what you said, i just used different notation

Answer 8

to pick four red balls right
so would i just add 7C5 to 7C4 x6C1

ie

7C5 + (7C4x6C1) ?

Answer 9

yes

Answer 10

and thats the answer, its that easy?