Question

Can someone please solve please?

Answer 1

Answer:495

Explanation:

Combinations formula:

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

Where n is the total number of units (books: 12 in this case) and r is the number of groups to combine (4 in this case)

Therefore:

₁₂C₄ = 12!/4!(12-4)! = 12!/4!*8!

just to explain:

= (12*11*10*9*8*7*6*5*4*3*2*1)/(4*3*2*1)*(8*7*6*5*4*3*2*1)

=(12*11*10*9)/(4*3*2*1) = (3*11*5*3) = 9*11*5 = 99*5 = 495

Answer 2

495

Explanation:

This problem can be solved b using a combination. We're using a combination for this because the order in which you would pick the books doesn't matter. To solve, we would plug in the number of books, in this case 12, into the n value of the combination. Then we would plug in the number of books that would be picked, in this case 4, into the r value of the combination. Solve the combination, and you get 495.