In the first hour of a bake sale, students sold either chocolate chip ...
As you get started on this problem, remember that with problems asking for a ratio between two unknowns that you often need much less information than you do for problems that ask for exact values. Students who do well on this problem will leverage this information and manipulate the statements in order to get as much information from them as possible.
Statement (1) gives a weighted average of the items sold. While this may seem to not give enough information, remember that weighted averages are essentially another way of expressing the ratio of the “weight” of two categories in an average – and because this “weight” is determined by the ratio of the number of items in each category, you can use this to solve for the ratio of cookies sold to brownies sold. If you recognize this, you can go ahead and determine that Statement (1) is sufficient. However, if y you don’t immediately recognize this, you can go ahead and solve for the ratio.
One easy way to illustrate this is with the Mapping Strategy, which can be set up as below, where Categories 1 and 2 are Cookies sold and Brownies sold, respectively.
Category 1 ---------Distance 1 ----------- Average -------Distance 2 ------ Category 2
Inserting what you know and finding the distance between each gives you
Cookies ------ 0.12 ------- 1.42 -------0.08 ------- 1.5
The ratio of the distances is therefore 12:8, which simplifies to 3:2. The ratio of the distances is always the inverse of the ratio between the amounts, so the ratio of the number of cookies sold to brownies sold is 2:3. Statement (1) is sufficient – eliminate "Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked", "Both statements (1) and (2) TOGETHER are sufficient to answer the question asked; but NEITHER statement ALONE is sufficient", and " Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed".
Statement (2) gives that the total value of items sold was $14.20. This strikes many students immediately as insufficient, leading them to pick "Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked". However, don’t forget to leverage your assets! Because you can only have whole numbers, there are only so many combinations of brownies and cookies sold that could give you $14.20 – it pays to experiment to see if there is in fact only one solution. While you should never “bring down” information from a previous statement, you can “borrow” from another to give you a place to start experimenting. Notice that the total amount, $14.20 is ten times the average price given in statement (1). This means that you could conclude that there could be a total of ten items sold. Using this information, you can set up two equations:
1.3C + 1.5B = 14.20
And
C + B = 10
Notice that you have a system of equations. Remember that if you solve a (non-dependent) linear system, you will get only one value each for C and B, meaning that you will have a consistent ratio. So it is possible to solve for one ratio. You don’t need to solve since you already know that there is a ratio that works with this number based on your work on Statement (1) – 2:3. The question is whether it is possible to have others.
What if, for example, there were 11 items? One way to “test the limits” of this is to ask if it would be possible to have 11 of any combination of items. If, for example, there were 11 chocolate chip cookies sold (the less expensive item), you would get:
(11)(1.3) = $15.40.
Because this is greater than the given price, $14.20, you should recognize that it is impossible to have a total of $14.20 with eleven items sold.
Similarly, you can test 9 or fewer items by seeing if it is possible to get to a total of $14.20 with 9 of the more expensive brownies. That would give you:
(9)($1.5) = $13.50
This means that there is no way to reach a total of $14.20 by selling 9 items. You can therefore conclude that the ratio from 10 items is the only possible one since you can’t sell a fraction of a brownie or cookie. Therefore, Statement (2) is sufficient. Eliminate "Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked" and choose answer choice "EACH statement ALONE is sufficient to answer the question asked".