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how many bit strings of length 10 contain exactly six 1s?

Sagot :

9514 1404 393

Answer:

  210

Step-by-step explanation:

The number of combinations of 10 things taken 6 at a time is ...

  10!/(6!(10-6)!) = 210

210 bit strings of length 10 will have 6 1-bits.

Using combination

[tex]\\ \sf\longmapsto {}^{10}C_6[/tex]

We know

[tex]\boxed{\sf {}^nC_r=\dfrac{n!}{r!(n-r)!}}[/tex]

[tex]\\ \sf\longmapsto \dfrac{10!}{6!(10-6)!}[/tex]

[tex]\\ \sf\longmapsto \dfrac{10!}{6!(4!)}[/tex]

[tex]\\ \sf\longmapsto 210[/tex]