Official ExplanationFor this problem you may find it helpful to translate the given information into an algebraic expression. Since the price of the book is unknown, you can call it x dollars, and then the total amount that Mary paid is x dollars plus 4% of x dollars, or 1.04x dollars. The problem states that Mary received some change from a $10 bill, so 1.04x dollars must be less than $10. Since the change was less than $3.00, the total amount Mary paid for the book must have been greater than $7.00. You can express this information algebraically by the inequality
\(7.00<1.04x<10.00\)
Solving the inequality for x by dividing by 1.04, and rounding, you get
\(6.73<x<9.62\)
So you see that x, the price of the book, must be between $6.73 and $9.62, and each price in between is possible. With this information, you can quickly examine the first two statements. Choice A is not necessarily true because the price could be as high as $9.61, and Choice B is not necessarily true because the price could be as low as $6.74.
To examine Choice C, you could compute the tax for the greatest possible price, which would be 4% of 9.61, or . Since this greatest possible tax is less than $0.45, Choice C must be true. You can also quickly see that Choice C must be true if you note that 4% of $10.00 would only be $0.40, and since the price must be less than $10.00, the tax must be less than $0.40.
The correct answer consists of Choice C.