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Isn't (1) by itself sufficient to answer the question ? The only positive integer values of x and y that satifsy 0.15x+0.29y=4.40 are x=y=10.

Hey coolwaether999.. you are cool (right). Only 1 combination works that way.. So A is alone suff. How do you figure out these kind of solution ? I am sure, trial and error will consume lot of time ... do you just hear your ear on that ..?

But the OA that I have says the the correct ans as D. I am just not able to figure out how B alone suff..
can anyone shed some light..

Re: DS : Set 6, Q30 - Joanna and her stamps [#permalink]

Show Tags

16 Sep 2007, 01:33

gluon wrote:

Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy?

(1) She bought $4.40 worth of stamps.

(2) She bought an equal number of $0.15 stamps and $0.29 stamps.

S1)

$4.40--> 440 We know that 15(x) +29(y)=440. Since 440 has a 0 on the end of it we have to have 29(y) equal to a number that will give us 0 on the end. Since the other number is 15 we must multiply 29 by a number that will give us a 0 as the units digit.

29*10=290. 15*10=150 150+290=440. The only number that satisfys this condition for 29 is 10. Since 20*29 is too great.

Suff.

S2)

This has to be insuff. Ok so the number is equal... so what... we aren't given any constraints as in S1. I really don't see how this can be suff since we can have an infinite number of values.

Could have 5 stamps of .15 thus 5 stamps of .29. could have 15 stamps of .15 thus 15 of .29. These give us different values.

Yes. D is the answer.
Both the statements by themselves are sufficient.
It took some time, but trial and error seemed to be the only way for me to arrive at making St. 1 suff.
St. B is simple algebra.

Amit05 wrote:

coldweather999 wrote:

Isn't (1) by itself sufficient to answer the question ? The only positive integer values of x and y that satifsy 0.15x+0.29y=4.40 are x=y=10.

Hey coolwaether999.. you are cool (right). Only 1 combination works that way.. So A is alone suff. How do you figure out these kind of solution ? I am sure, trial and error will consume lot of time ... do you just hear your ear on that ..?

But the OA that I have says the the correct ans as D. I am just not able to figure out how B alone suff.. can anyone shed some light..

Re: DS : Set 6, Q30 - Joanna and her stamps [#permalink]

Show Tags

16 Sep 2007, 03:45

gluon wrote:

Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy?

(1) She bought $4.40 worth of stamps.

(2) She bought an equal number of $0.15 stamps and $0.29 stamps.

how can 1 be alone sufficient. We cannot simply say she bought x numer of stamps of each how do we know that she bought equal number of stamps from 1 how can 2 be alone suffuicient. we do not know how much she spend.

I got it wrong while practising too and then the OA stunned me. I hate trick problems!!

Ravshonbek... I agree with you that we should not assume that x = y for (1). But if you look closely we dont need to.

This is a very tricky problem. We know that 0.15x + 0.29y = 4.40

If this was a generic equation then we could have x = -1 and y = (4.55/0.29)

But, since Joanna is buying stamps it is implicit that x and y are positive integers. Joanna cannot buy -1 or (4.55/0.29) stamps. The only positive integers that satisfy this equation are x = 10, y = 10. Hence, (1) is sufficient.

If there are some other positive integers that satisfy this equation then we would be correct about (1) being insufficient.

Last edited by gluon on 16 Sep 2007, 07:40, edited 2 times in total.

Speed kills! Careless error!
St. by 2 itself is not suff. There could be innumerable combinations that could suffice the eqn. [Let the no. of stamps of $0.15 denomination be x and $0.29 deno. be y
Then x*$0.15+y*$0.29=?]

So, the trial and error will give the ans. A.
Only the combination of 10 each of the two stamps suffice st.1 Remember the no. of stamps has to be +ve integer.
Am not sure how B is suff.!

Artemov wrote:

Yes. D is the answer. Both the statements by themselves are sufficient. It took some time, but trial and error seemed to be the only way for me to arrive at making St. 1 suff. St. B is simple algebra.

Amit05 wrote:

coldweather999 wrote:

Isn't (1) by itself sufficient to answer the question ? The only positive integer values of x and y that satifsy 0.15x+0.29y=4.40 are x=y=10.

Hey coolwaether999.. you are cool (right). Only 1 combination works that way.. So A is alone suff. How do you figure out these kind of solution ? I am sure, trial and error will consume lot of time ... do you just hear your ear on that ..?

But the OA that I have says the the correct ans as D. I am just not able to figure out how B alone suff.. can anyone shed some light..