Answer:
8$
Step-by-step explanation:
Because the first car wash does not cause the price to to down, but the ones after it do, you need onltake away 7 dollars of the price because it has only been discounted 7 times. Therefore 15-7=8 so 8 dollars is the answer.
The answer is 13. To figure this out I used 10 notebooks sold as a guide. I knew the answer could not be 10, because $27.95/10 was not a number stopping in the hundredths place (or a true money amount).
I tried numbers greater than 10 using a trial and error strategy until I got to 13 notebooks sold and found that it $27.95 was divisible by 13 to get an answer between $2 and $3 ($2.15 exactly).
Answer:

Step-by-step explanation:
The given system is:


Since I prefer to use smaller numbers I'm going to divide both sides of the first equation by 3 and both sides of the equation equation by 6.
This gives me the system:


We could solve the first equation for
and replace the second
with that.
Let's do that.

Subtract
on both sides:

So we are replacing the second
in the second equation with
which gives us:





Now recall the first equation we arranged so that
was the subject. I'm referring to
.
We can now find
given that
using the equation
.
Let's do that.
with
:



So the solution is (8,-1).
We can check this point by plugging it into both equations.
If both equations render true for that point, then we have verify the solution.
Let's try it.
with
:


is a true equation so the "solution" looks promising still.
with
:


is also true so the solution has been verified since both equations render true for that point.
They are both correct in their computation
(28.5-28.5(.3))+.1(28.5-28.5(.3))=$21.945
28.5(.7)(1.1)=$21.945
And since they each have $22 to spend, they have enough to purchase the book.