The inventory of grape jelly on a store's shelves consists only of 2-ounce, 6-ounce, and 16-ounce jars. If the average jar size of the current inventory is 6.4 ounces, how many additional 2-ounce jars must be put on the shelves to reduce the average size to 6.0 ounces?
(1) The current ratio of 2-ounce to 6-ounce to 16-ounce jars is 15:27:8.
Theres is a relation between the three so we can find the common factor x in all of them as in if 15x, 27x and 8x are number of jars of 2-ounce, 6-ounce and 16-ounce jars respectively. Hence we can find the value of more 2-ounce that needs to be added by keeping other ones same so that avergae comes down to 6.
\(\frac{(15x * 2 + 27x*6 + 8x*16) }{ (15x + 27x + 8x)}\) = 6.4
But x takes any value greater than equal to 1 i.e. x = 1 or 2 or 3 ... all satisfy which is not possible
INSUFFICIENT.
(2) There are initially 7 more 2-ounce jars than 16-ounce jars.
Here's a catch. We may initially choose to eliminate this but this statement creates a boundation that eventually creates a mirage that it can give us the answer.
Taking a clue from the Statement 1, we see that the number of 2-ounce and 16-ounce jars can be 15 and 8(other false possibilities that we may think are 7 and 0 or 8 and 1 or 9 and 2 and so on.. ), however, other possibilities(except those that are mulitples of 15 and 8) would lead to non-integer value of 6-ounce jars which is not possible. This is because 6-ounce jars too would have to be considered which has to be in specific ratio(let is be anything) with both 2-ounce and 16-ounce jars. But the relation of 6-ounce jars to the other two is not given and neither can be found based on the imputs available.
INSUFFICIENT.
Together 1 and 2
To understand better, think of the ratio of sumproduct(number of jars and weight of each type of jars) and total number of jars being in the ratio 64/10. Here, number of jars is in the multiple of 10(10,20, 30, 40, ....) and we need to fine balance it so that in that ratio sumproduct is a multiple of 64.
If one brainstorms more it can be found that the minimum number of jars that satisfy the condition is 50(the clue from Statement 1 helps). Next then is 100 but it disregards the condition of 2-ounce jars being 7 more than 16-ounce bars.
SUFFICIENT.
HTHs.
Answer C.