The total amount that Mary paid for

Sam Kinsman

Hi there,

Happy to help!

Think of it like this: what was the lowest possible cost of the book? In other words, what is the lowest possible value for (price of book + tax)?

Well, the person paid with $10, and got less than $3 change.

If the person had received EXACTLY $3 change, then the price (plus tax) would have been:

$10 - $3 = $7

But we know that the change was less than $3. Therefore the price (plus tax) must have been more than $7.

Does that make sense?

Oct 13, 2018 • Reply

David Recine, Magoosh Tutor

That's exactly correct, Shahram. Nicely done. :)

Mar 8, 2018 • Reply

Sam Kinsman

Hi Ishaan,

The question says "Which of the following statements must be true?" Option A says "the price of the book was LESS than $9.50." So if we can show that the price of the book could be $9.50, then we would prove that answer choice A is wrong (i.e. answer choice A does not have to be true).

As Chris showed, if the price of the book is $9.50, then the tax would be $0.38, and the total price would be $9.88. So Mary pays with $10, and gets 12 cents change. That fits what the question described (her change was less than $3.00). So the price of the book can be $9.50, and A is not correct.

I hope this helps!

Aug 26, 2017 • Reply

Cydney Seigerman, Magoosh Tutor

Hi Pawan :)

It looks like your inequality matches the information in the prompt:

7 < 1.04x

where x is the price of the book.

And if we plug in either $9.50 (to test A) or $6.90 (to test B), we can see that the book could be either of these prices and the inequality would hold true. Therefore, we can conclude that A and B do not necessarily have to be true.

On the other hand, we cannot use the inequality directly to test (C), which discusses the sales tax of the book and not the price of the book itself. For (C), the approach Chris goes over in the lesson video directly tests the sales tax, using the maximum possible value of the book as a starting point.

Apr 16, 2017 • Reply

Cydney Seigerman, Magoosh Tutor

Hi Inmobi :)

I'm happy to help! Let's look at (A) and (B) to see why they're not correct :)

A. The price of the book was less than $9.50

If the book cost $9.50, then the sales tax would be 4% of this price or $0.38 (9.5*0.04). The total price of the book plus tax would be $9.88, in which case if Mary paid with a $10 bill, she would receive $0.18 back as change. This amount is less than $3, meeting the requirements of the question. In other words, the price of the book could be $9.50 and therefore does not have to be less than $9.50.

B. The price of the book was greater than $6.90.

To see if this statement must be true, let's consider when the price is equal to $6.90. In that case, the tax would be 4% of $6.90 or 27.6 cents. Let's round the cents up to 28 cents. So, the total cost of the book plus tax would be

$6.90 + $0.28 = $7.28

And if Mary paid with a $10 bill, she would receive $2.72 as change, which is less than $3. Therefore, the book could cost $6.90 and (B) is therefore not correct.

I hope this clears things up :)

Jun 10, 2016 • Reply

Sam Kinsman

Hi Qingxiang, if the price of the book were $10, the sales tax would be $0.40. If the price of the book is lower than $10, the sales tax will be lower as well.
Mary paid with a $10 bill and got change, so the total cost of the book must be less than $10. Therefore, we know that the sales tax has to be lower than $0.40 - so we know option C is correct.

Oct 9, 2015 • Reply

chang feli

but option C is less than 0.45, then between 0.4 and 0.45, the condition is not valid. right?

Oct 25, 2018 • Reply

Adam Lyons, Magoosh Tutor

Hey Chang, we know for sure that the tax paid was less than $0.40. This means that it is most assuredly less than $0.45, no matter what. The sales tax is less than $0.45, and that is all that option C mentions. Thus, option C is true. It does not say anything about between $0.40 and $0.45, and since we know the tax is less than that, we don't have to think about that range at all.

Oct 29, 2018 • Reply