PLEASE HELP! Which is greater -6.875 or -6.89...
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Hello!
Set two variables for this situation. Let c = the cost of the chemistry book, and p = the cost of the physics book.
Create equations for the two statements seen here.
A chemistry book costs $6 less than a particular physics book: c + 6 = p
Two chemistry books and three physics book equal $123: 2c + 3p = 123
Now, set up your system of equations.
To solve, you're looking to use the substitution method. This method first takes an equation, and solves for a certain variable with it, and then substitutes in the equation for that certain variable into the other equation. That explanation was confusing, but hopefully it gets clearer here:
Since c + 6 = p, substitute c + 6 into the other equation for p.
2c + 3p = 123
2c + 3(c + 6) = 123
And now solve for c.
2c + 3(c + 6) = 123
2c + 3c + 18 = 123
5c = 105
c = 21
To find the other variable, just substitute c in one of the original equations.
c + 6 = p
21 + 6 = p
p = 27
Therefore, you have your solution. The chemistry book costs $21, and the physics book costs $27.
Hope this helps!