The only gift certificates that a certain store sold yesterday were

(1) The gift certificates sold by the store yesterday were worth a total of between $1 ,650 and $1,800.

Suff as only one combination of $100 and $10 GC is possible for total ranging from 1650-1800 i.e 17 ($100) and 3 ($10) total 1730, all other combinations within this range do not meet total number of GC condition

(2) Yesterday the store sold more than 15 gift certificates worth $100 each

Insuff as more than 15 can mean 16 and 4, 17 and 3, 18 and 2

THerefore A

Hi,

Difficulty level: 600

Number of gift certificates worth $100 = x
Number of gift certificates worth $10 = y
and x+y=20
Statement (1)
1650 < x+y < 1800 This gives us only one possible solution... 1730
Since there has to be 20 gift certificates and x=100$ and y=10$, 1730 is the only number that is between 1650 and 1800 that corresponds with 20 gift certificates
Every other solution is out of range e.g. 16 x 100$ + 4 x 10$ = 1640$ or 18 x 100$ + 2 x 10$ = 1820$, both out of the range 1650 < x+y < 1800

Statement (2) clearly insufficient since you can have more than one possible solution.

x+y = 20

st1.) 1650<100x+10y<1800
with ths eqn and x+y = 20
sufficient

st.2) x>15
not sufficient

Answer A.

Is this a trap question?

That is the intentions of the writer is to make you think that you need 1 and 2 to be able to get the correct answer.

because 2 is obviously not correct and if you weren't able to do 1 properly, you would have to automatically assume that 2 is required.

It seems like it is always advantageous to simply pick the A (or whatever is the harder stem) in these types of questions.

Yes, this question pretty much wants you to understand that A alone is sufficient, otherwise the fallback answer would be C. St II is obviously not sufficient by itself.

Here is a visual that should help.

Nearly every GMAT question can be solved by algebra, plugging in numbers, both, or a combination of the two. If you have time, then it's best to try both.

This particular method is a hybrid of the two: use algebra to get closer to conceptual understanding, then plug in numbers to test.

I approached 1 differently than the posts. Hopefully it helps.

(1) Given that 20 gift cards were sold... I saw 1,650 and tried to rationalize how to break that down. I know that I have to sell 16(100)+4(10) which is short of 1,650.

I progressed to 17(100)+3(10)=1,730 which checks out. 18(100)+2(10)=1820 which is outside the scope.

Therefore, I have only 1 possible answer. Sufficient

(2) Knowing nothing about (1), this is not sufficient by itself. So it cannot be B.

Knowing that (1) is sufficient, we no longer need (2). Not Sufficient

For these diophantine equations, it is actually possible to reduce the question pretty succinctly with algebra. Some people don't need to do that, and it does take a few extra seconds, but if you're interested this is how I did it.

Given:

100(A) + 10(B) = ?
A + B = 20

Statement 1:

100(A) + 10(B) = (1650, 1800) --> divide the whole equation by 10 to simplify.
10(A) + B = (165, 180) --> use the given information to substitute in for A.
10(20-B) + B = (165, 180)
200 - 9B = (165, 180) --> subtract 200 and divide by -1.
9B = (20, 35)

How many multiples of 9 are there between 20 and 35? Only one, so you know that B (which is an integer) can only take one value.

Statement 2:

There is more than one option for A and B, and the overall total is not constrained.

ANS: A

Let 10$ =x sales
100$ = 20-x

100(20-x) + 10x = total sales
2000-90x = TS

1) 1650<TS<1800
1650<2000-90x
-350<-90x
350>90x
x<3.something

and
2000-90x<1800
-90x<-200
90x>200
x> 2.something
=> x=3
DEFINITE x=3

2) 20-x>15
x<5
1,2,3,4 => insufficient

A is the answer

i believe this to be one of the "poster boy" questions for the gmat . While solving we should concentrate on the question rather than concentrating on the fact that the time is running out. Here goes the solution.
100x+10y=w and x+y=20

1. 1650<w<1800
x=16 then y=5 so putting this value in the 1st equation. not possible as 1650<w
x=17 then y=3 possible
x=18 then y=2 not possible as y<1800
2. not sufficient
A

We can let h = the number $100 gift certificates sold and t = the number of $10 gift certificates sold. Thus, we have h + t = 20, and we need to determine the value of t.

Statement One Alone:

The gift certificates sold by the store yesterday were worth a total of between $1650 and $1800.

We see that number of $100 gift certificates sold is no more than 17. That is, h ≤ 17.

If h = 17, then t = 3, and the total value of the gift certificates is 17(100) + 10(3) = $1730, which is between $1650 and $1800.

If h = 16, then t = 4, and the total value of the gift certificates is 16(100) + 10(4) = $1640. However, this is between not $1650 and $1800. Also, we don’t have to go any further down for the value of h, since we can see that from this point that there is no way the total value is between $1650 and $1800.

Therefore, we see that h must be 17 and t must be 3. Statement one alone is sufficient to answer the question.

Statement Two Alone:

Yesterday the store sold more than 15 gift certificates worth $100 each.

We see that h > 15, so h could be 16, 17, 18, 19 or 20 and t could be 4, 3, 2, 1, or 0, respectively. Since we don’t have a unique value for t, statement two alone is sufficient to answer the question.

Answer: A

If the store sold a total of 20 gift certificates yesterday, how many gift certificates worth $10 each did the store sell yesterday?

(1) The gift certificates sold by the store yesterday were worth a total of between $1,650 and $1,800.
It has to be a total of 20 Gift Certificates
16 *100 + 4*10 = 1610 <1650 does not satisfies statement 1
17*100+3*10 = 1710 >1650 and <1800 satisfies statement 1
18*100+2*10= 1810>1800 does not satisfies statement 1

(2) Yesterday the store sold more than 15 gift Certificates worth $100 each.

means number of $100 dollar certificates could be 16,17,18,19,20 different values of 100 could give different values of $10

Given: The only gift certificates that a certain store sold yesterday were worth either $100 each or $10 each.

Asked: If the store sold a total of 20 gift certificates yesterday, how many gift certificates worth $10 each did the store sell yesterday?

Let the number of gift certificates for $10 & $100 be t & h respectively.
t + h = 20 ; h = 20 - t (1)
Q. t=?

(1) The gift certificates sold by the store yesterday were worth a total of between $1,650 and $1,800.
$1650< 10t + 100(20-t) < $1800
1650 = 2000 - 90t < 1800
200<90t<350
2< 20/9< t <35/9 < 4
2 < t < 4
t = 3
3 gift certificates worth $10 each did the store sell yesterday
SUFFICIENT

(2) Yesterday the store sold more than 15 gift certificates worth $100 each.
h> 15
20 -t > 15
t < 5
t = {1,2,3,4}
NOT SUFFICIENT

IMO A

Video solution from Quant Reasoning:
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Nice trap question. I have done so many questions, but this is the first time I let the first statement influence the second.

The only gift certificates that a certain store sold yesterday were worth either $100 each or $10 each. If the store sold a total of 20 gift certificates yesterday, how many gift certificates worth $10 each did the store sell yesterday?

(1) The gift certificates sold by the store yesterday were worth a total of between $1,650 and $1,800.
We can deduce that 17 of the 100 certificates were sold.
Sufficient.

(2) Yesterday the store sold more than 15 gift certificates worth $100 each.
Careful here. We don't know the upper limit is 1800 anymore.
So, 16,17,18,19 of the 100 dollar tickets sold are all possibilities.
Insufficient.

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