Question

A pen holder holds ten pens, three of which do not write. If three pens are selected at random, find the probability that a least one writes

Answer 1

sounds binomial to me

Answer 2

at least one is the complement of at most none

Answer 3

\[1-\binom {10}0{p^0q^{10}}\]

Answer 4

i think i got my choosing off ...

Answer 5

3 choose 0, and q^3

the rest of it is to calculate p and q

Answer 6

or to look at it from a different point of view

we can pick 3 pens as: w = write, d = not write

www

wwd
wdw
dww

wdd
dwd
ddw

ddd

at least 1 dead is 1d + 2d + 3d

at least 1 writes is 1w + 2w + 3w