Answer:
Step-by-step explanation 10 + 2.50d = 850
David starts with $10 and each day he earns $2.50. The d represents a variable and can be any number.
To find d you must solve the equation.
10 + 2.50d = 850
2.50d = 840 (subtract 10 from 850)
d = 336 (divide 840 by 2.50)
It will take David 336 days to save $850.
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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Okay i haven't done this years but base on my knowledge it think that the answer is 6 and that because:
(2x+3) + (3-2x)
(2x+2x+3) +(3-2x+2x) (what ever you to one side you do the next and that why it cancel each other)
3+3=6
that my explanation hope this help