Question

So I have to compute the following but i don't know what they mean any help?

Answer 1

(a) 5

(b) 10

(c) 35

(d) 28

(e) 9

(f) 21

Explanation:

`((n)/(k) )=(n!)/(k!(n-k)!)`

(a)

`((5)/(1) )=(5!)/(1!(5-1)!) \\\\((5)/(1) )=(5*4*3*2*1)/(1*4!) \\\\((5)/(1) )=(120)/(1*4*3*2*1) \\\\((5)/(1) )=(120)/(24) \\\\((5)/(1) )=5`

(b)

`((5)/(3) )=(5!)/(3!(5-3)!) \\\\((5)/(3) )=(5*4*3*2*1)/(3*2*1*2!) \\\\((5)/(3) )=(120)/(3*2*1*2*1)\\\\((5)/(3) )=(120)/(12) \\\\((5)/(3) )=10`

(c)

`((7)/(4) )=(7!)/(4!(7-4)!) \\\\((7)/(4) )=(7*6*5*4*3*2*1)/(4*3*2*1*3!) \\\\((7)/(4) )=(5040)/(4*3*2*1*3*2*1) \\\\((7)/(4) )=(5040)/(144) \\\\((7)/(4) )=35`

(d)

`((8)/(2)) =(8!)/(2!(8-2)!) \\\\((8)/(2)) =(8*7*6*5*4*3*2*1)/(2*1*6!) \\\\((8)/(2)) =(40320)/(2*1*6*5*4*3*2*1)\\\\((8)/(2)) =(40320)/(1440) \\\\((8)/(2)) =28`

(e)

`((9)/(8) )=(9!)/(8!(9-8)!) \\\\((9)/(8) )=(9*8*7*6*5*4*3*2*1)/(8*7*6*5*4*3*2*1*1!) \\\\((9)/(8) )=(362880)/(40320*1!) \\\\((9)/(8) )=(362880)/(40320*1) \\\\((9)/(8) )=(362880)/(40320) \\\\((9)/(8) )=9`

(f)

`((10)/(4) )=(10!)/(4!(10-4)!) \\\\((10)/(4) )=(10*9*8*7*6*5*4*3*2*1)/(4*3*2*1*6!) \\\\((10)/(4) )=(3628800)/(24*6*5*4*3*2*1) \\\\((10)/(4) )=(362880)/(17280) \\\\((10)/(4) )=21`

Answer 2

Explanation:

This is a Combination (as in permutation vs combination) question the symbol (n r) refers to "n choose r". This is sometimes written as nCr

i.e the question is asking you to find how many combinations each will yield when you chose r items from n item without repetition and order does not matter.

I will only do the first question for you and you can just follow the same steps to solve the rest of the questions.

Recall that

`nCr=(n!)/((r!)(n-r)!)`

Consider question a) we are given (5 1) or ₅C₁

we can see that n = 5 and r = 1

If we substitute this into the formula:

₅C₁ = (5!) / [ (1!)(5- 1)!]

= (5!) / [ (5- 1)!]

= (5!) / (4!)

= (5·4·3·2·1) / (4·3·2·1)

= 5

hence ₅C₁ = 5