Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Can't understand how to get the answer from (2). Do we consider that dogs and pets are only animals in the shop?

Not so. We are told that \(\frac{1}{3}\) of the pets are dogs and \(\frac{1}{5}\) of the pets are birds --> \(\frac{1}{3}+\frac{1}{5}=\frac{8}{15}<1=total\).

At a certain pet shop, 1/3 of the pets are dogs and 1/5 of the pets are birds. How many of the pets are dogs?

(1) There are 30 birds at the shop --> \(\frac{1}{5}\) of the pets are birds --> \(\frac{1}{5}t=30\), where \(t\) is the # of pets at the pet shop --> \(t=150\) --> \(\frac{1}{3}\) of the pets are dogs --> there are \(\frac{1}{3}*150=50\) dogs at the pet shop. Sufficient.

(2) There are 20 more dogs than birds at the pet shop --> \(d=b+20\) --> \(\frac{1}{3}t=\frac{1}{5}t+20\), where \(t\) is the # of pets at the pet shop --> \(t=150\) --> \(\frac{1}{3}\) of the pets are dogs --> there are \(\frac{1}{3}*150=50\) dogs at the pet shop. Sufficient.

Can't understand how to get the answer from (2) Do we consider that dogs and pets are only animals in the shop?

To answer your question, no we do not consider that dogs and birds are the only animals at the shop. In fact, we know they are not because \(\frac{1}{3} + \frac{1}{5} = \frac{8}{15}\). So dogs and birds account for only 8/15th of the total animals.

Now, let's solve this question using ratios.

Dogs : Birds = \(\frac{1}{3} : \frac{1}{5}\). Multiply this ratio by 15 to convert it into integers. Remember, when you multiply the entire ratio by the same number, the ratio remains the same.

Dogs : Birds = 5:3. For every 3 birds, there are 5 dogs. Stmnt 1: If birds are 30, dogs will be 50. Sufficient. Stmnt 2: The difference in number of dogs are birds in ratio terms is 2 (because 5 - 3 = 2), but is actually 20. So 5 will correspond to 50. Sufficient.

Ratios are a great way to quickly and easily solve questions. If this method is not clear, give me a couple of days. I will put up a blog explaining it in detail.
_________________

Does this assume that there are only dogs and birds in the pet shop? If so, shouldn't the problem state it?

If 1/3 of the pets are dogs, and 1/5 of the pets are birds, then only 1/3 + 1/5 = 8/15 of all pets are dogs or birds. So 7/15 of the pets need to be something other than dogs or birds. So no, the question is not assuming there are only dogs and birds in the shop.
_________________

GMAT Tutor in Toronto

If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com

Re: At a certain pet shop, 1/3 of the pets are dogs and 1/5 of [#permalink]

Show Tags

01 Sep 2014, 19:13

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Re: At a certain pet shop, 1/3 of the pets are dogs and 1/5 of [#permalink]

Show Tags

18 May 2016, 11:27

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Please help with the following DS Q: At a certain pet shop, 1/3 of the pets are dogs and 1/5 are birds. How many of the pets are dogs? (1) There are 30 birds at the pet shop. (2) There are 20 more dogs than birds at the pet shop.

I answered A, but the right answer seams to be D. Any one can help why statement 2 is also sufficient?

Please help with the following DS Q: At a certain pet shop, 1/3 of the pets are dogs and 1/5 are birds. How many of the pets are dogs? (1) There are 30 birds at the pet shop. (2) There are 20 more dogs than birds at the pet shop.

I answered A, but the right answer seams to be D. Any one can help why statement 2 is also sufficient?