abrutlag wrote:
David earns a commission that consists of a certain number of dollars per sale, plus a fixed percent of the dollar amount of the sale. Is his commission on a 250,000 dollar sale at least 20,000 dollars?
(1) His commission on a 300,000 dollar sale is at least 30,000 dollars.
(2) His commission on a 100,000 dollar sale is at least 10,000 dollars.
x = fixed commission per sale
y = percent of sales amount
For a sale of 250,000, David earns x + y/100(250,000). The problem asks if this is at least 20,000. This simplifies to, is x+2,500y ≥ 20,000?
(1)
The problem asks if David's commission was greater than 20,000. So, try to make the commission as small as possible and see if it is still greater than 20,000.
To make the commission as small as possible, assume that his commission on a 300,000 sale was exactly 30,000. So, x + y/100(300,000) = 30,000. This simplifies to x + 3,000y = 30,000.
Therefore, y = 30,000-x/3,000. Plug this into the question.
Is x + 2,500(30,000-x/3,000) ≥ 20,000?
Is x + 2,500(10 - x/3,000) ≥ 20,000?
Is x + 25,000 - 25/30x ≥20,000?
Is 5/30x ≥ -5,000?
Because x is positive (David's commission must be positive), then this is always true and the answer is "yes"
SUFFICIENT
Note that if you substitute differently, the math becomes more complicated, but you can still find the same answer. Try substituting for x instead:
x + 3,000y = 30,000
x = 30,000-3,000y
Plug this in to the question
Is 30,000 - 3,000y + 2,500y ≥ 20,000?
Is 30,000 - 500y ≥ 20,000?
Is 10,000 ≥ 500y?
Is y ≤ 20?
This means, if y ≤ 20, the answer is "yes". But, remember what y represents. y is the percent of sale that David earns as a commission So, if y is GREATER than 20, then David earns more than 20% of 250,000, which is much greater than 20,000. So, the answer is still "yes".
SUFFICIENT
(2) This statement could mean that x = 10,000 (he earns 10,000 per sale plus 0% of the sale). So, his commission on a 250,000 sale would also be 10,000, and the answer would be "no"
Or, it could mean that x = 0, and y = 10%. So, his commission on a 250,000 sale would be 10% of 250,000, which is 25,000. The answer would be "yes"
NOT SUFFICIENT