Question 861886
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Hi
{{{15}}} balls:6 black, 4 white and 5 green balls
In how many ways can 3 balls be selected if at least 2 balls are black?
{{{ 6C3 + (6C2)(4C1) + (6C2)(5C1) = 20 + 15*4 + 15*5 = 20 + 60 + 75 = 155}}}

Using a calculator to find {{{nCx = (n!)/x!(n - x)!)}}} 
for ex: TI-83 calculator,
enter 5, press MATH,
PRB, 3:nCr
ENTER.