There are 5 blue crayons, 7 yellow crayons, and 8 red crayons. in a box. If one is randomly drawn and replaced 15 times, find the probability of drawing exactly four blue crayons?

1 Answer
MattyMatty
May 1, 2018

#0.2252#

Explanation:

#"There are 5+7+8 = 20 crayons in total."#
#=> P = C(15,4) (5/20)^4 (15/20)^11#
#= ((15!) 5^4 15^11) / ((11!)(4!) 20^15)#
#= 0.2252#

#"Explanation :"#
#"Because we replace, the odds for drawing a blue crayon are"#
#"each time 5/20. We express that we draw 4 times a blue one"#
#"and then 11 times not a blue one by (5/20)^4 (15/20)^11."#
#"Of course the blue ones do not have to be drawn first so there"#
#"are C(15,4) ways of drawing them, so we multiply by C(15,4)."#

#"and C(15,4) "= (15!)/(11!4!) " (combinations)"#

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