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Each packet of computer floppies contains a coupon that is equally likely to bear the letters D, E or F. If `x` packets are purchased, what is the probability that the coupons cannot be used to spell `FED`?

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probablity of coupon have either of the following alphabets is 1/3
probablity a coupon is not D or it is not E or it is not F is 2/3

probability of x number of couple not having D in then = (2/3)^x

probability of x number of couple not having E in then = (2/3)^x

probability of x number of couple not having F in then = (2/3)^x

to spell FED we coupon of every alphabet

probabilty spell FED is possible = 1 - probablity spelling FED is impossbile ( that is one of the alphabets is missing )

probabilty of one of the alphabet missing = probablity of D missing + probablity of E missing + probablity of F missing

probabilty spell FED is possible = 1 - 3*(2/3)^x
13 years agoHelpfull: Yes(0) No(1)

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