Andres bought exactly two sorts of donuts, old-fashioned donuts and je

Question

Andres bought exactly two sorts of donuts, old-fashioned donuts and jelly donuts. If each old-fashioned donut costs $0.75 and each jelly donut costs $1.20, how many jelly donuts did Andres buy?

(1) Andres bought a total of eight donuts.
(2) Andres spent exactly $7.35 on donuts.

Barnal · Answer

Ok, let's try to explain :

Let's pick N  for the number of old fashion donuts, N  jelly donuts

Total price = N *0.75 + N  * 1.2

(1) gives us : N +N =8 -> we still have 3 unknowns and 2 equations INSUFICIENT

(2) gives us : 7.35=N *0.75 + N  * 1.2 -> we still have 3 unknowns and 2 equations INSUFICIENT

(1) + (2) -> 3 equations for 3 unknowns we can solve the problem.

Answer C for me

shreyast · Answer

I'll give this question a 700 rating based upon time it takes to solve it.

Answer B. (2) alone is sufficient.

Solution::
We know (1) alone is not sufficient. Let's try (2) -

Since the total amount spent ends in 5, we know that old-fasioned donuts (ODFs) will be odd. (Since they cost 75 cents each).
So total amount spent on OFDs could be: 75 or 225 or 375 or 525 or 675 cents.
After spending that much amount remaining amount had been spent on jelly donuts (JDs);
so the corresponding amount will be 660 or 510 or 360 or 210 or 60 cents.

Clearly, only 375 + 360 cents option matches with the total amount spent. Hence option B. If there were more than one options correct, then we could've said C.

smashbiker84 · Answer

Ans: B

stmnt 1: absolutely not sufficient. NO Price constraint. can buy any quantity of each type as long as total of 8 donuts are bought .

Stmnt 2 : eqn is 0.75O + 1.2J = 7.35 . Simplifying ( remove decimals and factor out 15 both sides) yields 5O + 8J = 49. Number property of 5 says all its multiples will be either 0 or 5. if 0 then, 8 has to have a multiple ending in 9 to get required RHS. Impossible . so "5O" has to end with 5 and hence 8J has to end with "4" to yield the "9" of 49 . Only viable option is 25 & 24 (=8*3). So Andrea bought 3 jelly donuts. Sufficient

note: if price constraint was not given or was of larger amount, mutiple options could be possible in Stmnt 2 also.

chetan2u · Answer

hi  Barnal ,

at times we can find answer even though at first look at seems not possible..
this is often tested in DS..
as you can see in statement ll, 7.35 should be sum of .75 multiplied by an integer and 1.2 multiplied by an integer...
take multiples of 1.2 and subtract from 7.35 and this leftover should be a multiple of .75..
only one set of values satisfies the condition.. 3*1.2+.75*5=7.35... sufficient
ans B

Lucky2783 · Answer

(1) Andres bought a total of eight donuts.
 O+J=8 . Not sufficient .

(2) Andres spent exactly $7.35 on donuts.
 0.75 * O + 1.2 * J = 7.35 
 75O + 120J = 735 
 5O + 8J = 49
 O=5 J=3only one set of values satisfies this equation . 
 
Answer B.

Barnal · Answer

Hello Chetan2u, That's right, I might have not seen this as I want to get as quick as I can. I fell in the trap... I might keep training ! Anyway, thanks to the GMAT CLUB, I will reach my goal

AVRonaldo · Answer

Clearly statement 1 is insufficient . total number of donuts = 8 does not help in finding the total number of jelly donuts.

Translating the question stem and statement 2, we have

d- old fashioned donuts
j - jelly donuts

==> 0.75d + 1.20j = 7.35

Since the number of donuts has to be an integer, we have an integer constraint here.

Subtract 0.75 from 7.35 and try dividing it by 1.20 to check if its divisible. Keep this process going till you find the multiple.
7.35 - 0.75 = 6.60 is not divisible by 1.20
6.60 - 0.75 = 5.85 is not divisible by 1.20
5.85 - 0.75 = 5.10 is not divisible by 1.20
5.10 - 0.75 = 4.35 is not divisible by 1.20
4.35 - 0.75 = 3.60 is divisible by 1.20

(5)0.75 + (3)1.20 = 7.35 ==> No of jelly donuts = 3

Hence Statement 2 is sufficient

Answer is (B)

DmitryFarberMPrep · Answer

Yes, this problem has a C Trap, but here's how to avoid it: know the answer in advance! I'm not kidding. Statement 1 is not helpful by itself, and the two statements can be combined fairly easily to get the answer. However, an answer of C is simply too good to be true. If that's the case, the answer must be B!

Once you realize this, you can go into statement 2 expecting that this particular price can only come about one way. It helps that one of the numbers ends in 5 and the other doesn't, so there are only so many combinations that might work.

There are many examples of C Traps in official materials. Here are three from the OG: 110, 119, and 132.

SherLocked2018 · Answer

First look at 2 options gives C as an easy ans. But usually in such Qns, C is not correct. 
1) alone is definitely not suff, since we dont have complete info about the total cost. 
2) since we know total cost is 7.35, and each individual donut cost, we find a distribution of .75 and 1.2 whch gives 7.35. (calculate for a couple of values by hit and trial)
we get 5*.75 + 3*1.2 = 3.75 + 3.6 = 7.35. and no other value gives this total, (since we cant have -ve values.) 
I calculated for : (OD = 1,2,3 and got on 3rd, tried for 4th and was not getting total = 7.35) 
Thus B is sufficient.

Bunuel · Answer

This is an example of a C-Trap question. For more check  HERE  (theory and practice questions).

SavageBrother · Answer

I did it by picking numbers, not the most efficient, but it works.

1) - no information about the price
2) 7.35 total, strange number in combination with the prices of donuts

O = old fashion
J = Jelly donut

0,75O + 1,2J = 7,35
5*0,75 = 3,75
3*1,2 = 3,6

3,75 + 3,6 = 7,35

B.

Sidhrt · Answer

Hi buddy its Bunuel not Barnal. Lets right the name correctly and show some respect for the people from whom we learn.

chetan2u · Answer

Hi buddy its Bunuel not Barnal. Lets right the name correctly and show some respect for the people from whom we learn.

hi buddy, you require to check the posts before commenting. there can be someone named Barnal too. lets not be mean and give respect only for those whom we gain from.... and try to learn from everyone as there is something to learn from everyone.... I just learned from you not to jump the gun....and by the way it is not right , it is write

Sidhrt · Answer

hi buddy, you require to check the posts before commenting. there can be someone named Barnal too. lets not be mean and give respect only for those whom we gain from.... and try to learn from everyone as there is something to learn from everyone.... I just learned from you not to jump the gun....and by the way it is not right , it is write

Hahaha, i preassumed something like this for a typo mistake. Anyway maturity demands that I conclude it further with an apology note for the name confusion.

chetan2u · Answer

hi  Sidhrt ,
Its perfectly fine. hope you are having a good time with your GMAT preparations. Regards

Temurkhon · Answer

it is C trap question because it is clear that if we have two variables and two equations, we will get the answer

St.1 is INSUFF

St2. we have 75x+120y=735

Maximum of 120*6=720, so we should go less number
120*5=600, but neither of 75 can give 135
120*4=480, means 75*x should equal 235, does not fit
120*3=360, means 75*x should equal 375, so x=5, y=3, SUFF

B

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Andres bought exactly two sorts of donuts, old-fashioned donuts and je

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