There are 6720 ways by 8 distinguishable books be placed in 5 shelves.
According to statement
The number of books (n) is 8
The number of shelves (r) is 5
Now, we find the ways by which the 8 books be placed in 5 distinguishable shelves
From Permutation formula
P(n,r) = n! / (n-r)!
Substitute the values then
P(n,r) = 8! / (8-5)!
P(n,r) = (8*7*6*5*4*3*2*1) / (3*2*1)
P(n,r) = 8*7*6*5*4
P(n,r) = 6720
So, there are 6720 ways by 8 distinguishable books be placed in 5 shelves.
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Plumber a = 60x
Plumber b = 40+55x
An 8 hour job would cost the same for both plumbers. It would cost $480. Plumber a should be hired for a 5 hour job.
Hi!
See my image for the answer.
I put each of the choices into the equation, then solved it.
The answer is B. (4,-12)
Hope this helps! :)
-Peredhel