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:

Concentration: Entrepreneurship, International Business

GMAT 1: 730 Q50 V39

GPA: 3.2

WE: Education (Education)

Re: What is the remainder when (47)(49) is divided by 8? [#permalink]

Show Tags

02 Mar 2013, 15:14

3

This post received KUDOS

4

This post was BOOKMARKED

Hello Mun23,

The easy way to solve such questions is to divide the numbers individually by 8 and then multiply the remainders. Confirm whether the product of the remainders can be divided by 8 again. If yes, then divide and find the remainder and that will be your answer. If not, then the product of the remainders is your answer.

Here are a few examples to show this.

Find the remainder of 15*9/4. 15/4 gives a remainder of 3 and 9/4 gives a remainder of 1. Hence, the total remainder is the product of the remainders=3 which cannot be further divided BY 4. Let us confirm this the long way. 15*9=135. Divide 135 by 4 and you get a quotient of 33 and a remainder of 3.

Similarly, try 21*9/7. 21/7 gives a remainder os 0 and 9/7 gives a remainder of 2. Hence, 0*2=0 is the total remainder. You can try this the long way.

Now, coming to the question at hand 47/8 gives a reminder of 7 and 49/8 gives a remainder of 1. 7*1=7 is the total remainder and thus, the answer is e.

Hope this helps! Let me know in case of any further questions.

mun23 wrote:

What is the remainder when (47)(49) is divided by 8? (A)1 (B)3 (C)4 (D)5 (E)7

Concentration: Entrepreneurship, International Business

GMAT 1: 440 Q33 V13

GPA: 3

Re: What is the remainder when (47)(49) is divided by 8? [#permalink]

Show Tags

03 Mar 2013, 01:12

2

This post received KUDOS

mun23 wrote:

What is the remainder when (47)(49) is divided by 8? (A)1 (B)3 (C)4 (D)5 (E)7

I have an alternate learnt here

\(Rof (47) (49)\) when divided by 8

Always reminder of product of two numbers divided by a divisor will be equal to product of reminders of corresponding numbers divided by same divisor

Using this rule, \(Rof (47)\) = 7 \(Rof (49)\) = 1

So\(Rof (47) (49)\) = 7*1 =7

Other way would be \(Rof (47)\) = -1 ( which is same as 7, but to do simpler we use -ve number 8-7) \(Rof (49)\)= 1 So\(Rof (47) (49)\) = -1*1 =-1 Therefor 8-1= 7

I'm missed the link from which i learnt this.. I'm searching for it.. Once i get it will post it up here !!
_________________

GMAT - Practice, Patience, Persistence Kudos if u like

Re: What is the remainder when (47)(49) is divided by 8? [#permalink]

Show Tags

28 Mar 2013, 01:34

1

This post received KUDOS

Let N = A * B and we would like to find the remainder when N is divided by D. A = aD + x where x is the remainder of A/D. B = bD + y where y is the remainder of B/D.

so N = (aD + x) * (bD + y) = abD\(^2\) + bxD + ayD + xy

So, N/D will give a remainder xy if xy < D.

Considering the above principle,

R1 = 47/8 = 7 R2 = 49/8 = 1 R = R1 * R2 = 7 * 1 = 7. Hence option E will be the correct answer.

---------------------------------------------------- Please press KUDOS if you like my post. _________________

Re: What is the remainder when (47)(49) is divided by 8? [#permalink]

Show Tags

03 Mar 2013, 00:30

47 x 49 = (48-1)(48+1) 47 x 49 = \(48^2 - 1^2\) therefore (47 x 49)/8 = (\(48^2 - 1^2\))/8 since remainder of a number can be expressed as the sum or difference of individual fractions hence rem(\(48^2 - 1^2\))/8 = rem(\(48^2\)/8) - rem(\(1^2\)/8) Now, Rem(48^2/8) = 0 and Rem(1^2/8) = 1 so we have rem(47)(49)/8 = -1 or (8-1 =) 7

Re: What is the remainder when (47)(49) is divided by 8? [#permalink]

Show Tags

14 Nov 2014, 07:21

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: What is the remainder when (47)(49) is divided by 8? [#permalink]

Show Tags

13 Jun 2017, 17:59

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.
_________________

Abhishek009, this method looks like a good one to learn. Two questions:

1. Did you choose to use 49/8 = remainder 9 instead remainder 1 so that you could get a two-digit number, 63? So that it was clearer than the single digit 7 (divided by 8, which = 0 + R7)?

2. Is it okay in problems like these to use a remainder that is bigger than the divisor?

What is the remainder when (47)(49) is divided by 8? (A)1 (B)3 (C)4 (D)5 (E)7

To start, we can separately divide 47 by 8 and 49 by 8.

47/8 = 5 remainder 7

49/8 = 6 remainder 1

To determine the remainder of the product of 47 and 49, we can multiply the remainders together and we have 7 x 1 = 7.

Alternate solution:

Notice that (47)(49) = (48 - 1)(48 + 1) = 48^2 - 1^2 = 48^2 - 1. Now notice that the first term, 48^2, is divisible by 8 since 48 is divisible by 8. Thus, the remainder will be the second term, -1. If a number has a remainder of -1 when it’s divided by 8, the remainder is actually -1 + 8 = 7.

Answer: E
_________________

Scott Woodbury-Stewart Founder and CEO

GMAT Quant Self-Study Course 500+ lessons 3000+ practice problems 800+ HD solutions