Last visit was: 21 Dec 2024, 03:15 It is currently 21 Dec 2024, 03:15

Close

GRE Prep Club Daily Prep

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 GRE 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.

Close

Request Expert Reply

Confirm Cancel
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Own Kudos [?]: 12231 [9]
Given Kudos: 136
Send PM
Verbal Expert
Joined: 18 Apr 2015
Posts: 30431
Own Kudos [?]: 36789 [0]
Given Kudos: 26094
Send PM
avatar
Manager
Manager
Joined: 28 Mar 2019
Status:Job holder
Posts: 108
Own Kudos [?]: 104 [0]
Given Kudos: 0
Location: Bangladesh
Mohammad Alamin Asif: Mohammad Alamin Asif
Send PM
Verbal Expert
Joined: 18 Apr 2015
Posts: 30431
Own Kudos [?]: 36789 [0]
Given Kudos: 26094
Send PM
Re: What is the remainder when [m]3^{32}[/m] is divided by 82? [#permalink]
Expert Reply
when you see the pattern the number 3^32 is huge but you need to care only of the unit digit.

the number is xxxxx7 divided by 82

7/2 the remainder is 1

hope now is clear
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Own Kudos [?]: 12231 [0]
Given Kudos: 136
Send PM
Re: What is the remainder when [m]3^{32}[/m] is divided by 82? [#permalink]
2
GreenlightTestPrep wrote:
What is the remainder when \(3^{32}\) is divided by \(82\)?

A) 0
B) 1
C) 8
D) 9
E) 81


If we recognize that 82 is 1 greater than 81 (aka \(3^4\)), then we might see that 82 is a divisor of \(3^{32} - 1\)
Here's why:

\(3^{32} - 1 = (3^{16} + 1)(3^{16} - 1)\)
\(= (3^{16} + 1)(3^8 + 1)(3^8 - 1)\)
\(= (3^{16} + 1)(3^8 + 1)(3^4 - 1)(3^4 + 1)\)
\(= (3^{16} + 1)(3^8 + 1)(3^4 - 1)(82)\)

This tells us that \((3^{32} - 1)\) is a multiple of 82...
...and this means \(3^{32}\) is 1 greater than a multiple of 82, which means we'll get a remainder of 1 when we divide \(3^{32}\) by 82

Answer: B

Cheers,
Brent
avatar
Intern
Intern
Joined: 02 Sep 2020
Posts: 14
Own Kudos [?]: 9 [2]
Given Kudos: 0
Send PM
Re: What is the remainder when [m]3^{32}[/m] is divided by 82? [#permalink]
2
Carcass wrote:
Good question but I am a witness of the eras: true I am old.

ten years ago a similar question for the gmat or gre was super tough. Now , if you do your home work, it is moderate

See the patter, no need fancy calculations

\(3^2=9\)
\(3^3=27\) (here what count for us is the unit digit = 7
\(3^4=..1\)
\(3^5=..3\)
\(3^6=..9\)

So the patter before to repeat itself is 9-7-1-3-9. We do need the 32nd position7 which is 7

7 divided by 2 (82 we care only of the unit digit) = 1

B is the answer



Hi Carcass,

As per me,its should be a cycle of 4 not of 3,I am not sure why you are considering units digit as 7 and taking 3rd power of 3.

3 raise to 1 is 3
3 raise to 2 is 9
3 raise to 3 is unit digit 7
3 raise to 4 is unit digit 1

3 raise to 32
32=8x4,i.e,8 cycles of 4

therefore 3 raise to 32 will have unit digit as 1 which when divided by 82 will yield 1

Originally posted by vaishar3 on 20 Sep 2020, 13:21.
Last edited by vaishar3 on 22 Sep 2020, 10:57, edited 1 time in total.
avatar
Intern
Intern
Joined: 07 Sep 2020
Posts: 15
Own Kudos [?]: 1 [0]
Given Kudos: 0
Send PM
Re: What is the remainder when [m]3^{32}[/m] is divided by 82? [#permalink]
pattern starts with 3^0?
avatar
Intern
Intern
Joined: 02 Sep 2020
Posts: 14
Own Kudos [?]: 9 [0]
Given Kudos: 0
Send PM
Re: What is the remainder when [m]3^{32}[/m] is divided by 82? [#permalink]
1
no Shubham,

In these questions,always start with power of 1 as it will give the first unit digit in the series of all the powers you are considering.Check my answer above.

Posted from my mobile device Image
Intern
Intern
Joined: 21 Oct 2024
Posts: 48
Own Kudos [?]: 2 [0]
Given Kudos: 1
Send PM
Re: What is the remainder when [m]3^{32}[/m] is divided by 82? [#permalink]
vaishar3, why unit digit is 7 and not 1? I understand that 32 is event. There are 8 blocks of 4 to come up with 32. Should we take 1 then?
Verbal Expert
Joined: 18 Apr 2015
Posts: 30431
Own Kudos [?]: 36789 [0]
Given Kudos: 26094
Send PM
Re: What is the remainder when [m]3^{32}[/m] is divided by 82? [#permalink]
Expert Reply
The power cycle is

9-7-1-3-9 and the power is 32

6*5=30

Therefore 30 cycles end with 9

+2 more is 9 and then 7

The number we are looking for is 7
Intern
Intern
Joined: 21 Oct 2024
Posts: 48
Own Kudos [?]: 2 [1]
Given Kudos: 1
Send PM
Re: What is the remainder when [m]3^{32}[/m] is divided by 82? [#permalink]
1
Carcass, can you please share an example of a similiar problem?
For some reason, I have an understanding that it is a cycle of 4 since 9 repeats and should not be included in the count.
Verbal Expert
Joined: 18 Apr 2015
Posts: 30431
Own Kudos [?]: 36789 [0]
Given Kudos: 26094
Send PM
Re: What is the remainder when [m]3^{32}[/m] is divided by 82? [#permalink]
Expert Reply
The cycle restarts at 9 so why we consider five.

32 turns of the cycle and you will land in the unit digit of 7
Verbal Expert
Joined: 18 Apr 2015
Posts: 30431
Own Kudos [?]: 36789 [0]
Given Kudos: 26094
Send PM
Re: What is the remainder when [m]3^{32}[/m] is divided by 82? [#permalink]
Expert Reply
Prep Club for GRE Bot
Re: What is the remainder when [m]3^{32}[/m] is divided by 82? [#permalink]
Moderators:
GRE Instructor
88 posts
GRE Forum Moderator
37 posts
Moderator
1115 posts
GRE Instructor
234 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne