Dashes being DOTS!!

Probability Level 2

The number of different ways in which 5 "dashes" and 8 "dots" can be arranged ,using only 7 of these 13 "dashes and dots" is

1235520 719 1287 120

Rajat Bisht by Rajat Bisht , 23, India

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1 solution

Bk Lim
Dec 18, 2014

For each of the 7 places, we can choose either dashes or dots, 2^7=128 choices.

But wait, 6 dashes and 7 dashes are not allowed.

128 - 7C6 - 7C7 =120

10 Helpful 4 Interesting 3 Brilliant 4 Confused

Not understood

Abhi Yadav - 4 years, 4 months ago

Plz explain

Krithika Bhattacharyya - 2 years, 2 months ago

It means coz there r only 5 dashes we cant have the case where 6 or 7 dashes r present so those cases have to be subtracted from 128

Dana Taylors - 2 years ago

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