If t is a postive integer and r is the remainder when t-squared+5t+6 is divided by 7, what is the value of r?
1) When t is divided by 7, the remainder is 6.
2) When t-squared is divided by 7, the remainder is 1.
How to solve this without taking heaps of time?
Thank you!
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A Question from GMAT prep exam
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(t^2 + 5t+6)/7 = t^2/7 + 5t/7 + 6/7
Looking at both 1 and 2 they are not enough , the only option is to combine them
from second statement t^2/7 has remainder 1 and 6/7 has remainder 6 so combining them (6+1) /7 will leave 0 remainder,
So if we find the remainder for 5t/7 we solve the puzzle
from statement 1, t= 7k + 6
Multiply by 5 => 5t = 35k + 30
5t/7=35k/7 + 30 /7
will always have remainder 2 as 30/7 leaves remainder 2
Choice C
Looking at both 1 and 2 they are not enough , the only option is to combine them
from second statement t^2/7 has remainder 1 and 6/7 has remainder 6 so combining them (6+1) /7 will leave 0 remainder,
So if we find the remainder for 5t/7 we solve the puzzle
from statement 1, t= 7k + 6
Multiply by 5 => 5t = 35k + 30
5t/7=35k/7 + 30 /7
will always have remainder 2 as 30/7 leaves remainder 2
Choice C
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Refer to
https://www.beatthegmat.com/t-2-5t-6-t20195.html
Morgoth has posted an excellent explanation (one of the best solutions that I have seen in this forum)
https://www.beatthegmat.com/t-2-5t-6-t20195.html
Morgoth has posted an excellent explanation (one of the best solutions that I have seen in this forum)
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Patiod,
Please post OA's using SPOILER function if possible at the same time that u post the questions.
Let me know if u still have any questions on the actual DS question also!
Regards,
Cramya
Please post OA's using SPOILER function if possible at the same time that u post the questions.
Let me know if u still have any questions on the actual DS question also!
Regards,
Cramya
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well if I understand you correctly, you already know how to solve this problem but you are looking for a faster approach.patio-d wrote:If t is a postive integer and r is the remainder when t-squared+5t+6 is divided by 7, what is the value of r?
1) When t is divided by 7, the remainder is 6.
2) When t-squared is divided by 7, the remainder is 1.
How to solve this without taking heaps of time?
Thank you!
[/img]
Question wants you to find R:
t-squared+5t+6 = 7(integer) + R
so in other words, if you can change the left side of the question into 7A+R format, R is your answer!
and you need to see that t-squared+5t+6 = (t+3)(t+2) in case!
1) t = 7a+ 6
(7a+9)(7a+8)divided by 7
(7a+7+2)(7a+7+1) ; so the remainder will always be 2.
SUFF
2) t-squared = 7b+1
t-squared - 1 = 7b
(t-1)(t+1) = 7b
t will have two values, and for each T value the Remainder will change
Insuf
IMO, hence A
It might be D , if I missed something in statement 2
LGTCH
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It is A and u did not miss D.
Building upon what was said above just as a double check....
(t+1) (t-1) = 7 (some integer)
Either t-1 is a multiple of 7 or t+1 is a multiple of 7
Lets say t+1 is a multiple of 7 ASSUME t=6
(t+1) (t-1) = 7 * 5 = 7 (some integer which is 5) The remainder for t+3 t+2 divided by 7 here would be 9 * 8 /7 REMIANDER 2
Lets say t-1 is a multiple of 7 ASSUME t=8
(t+1) (t-1) = 9 * 7 = 7 (some integer which is 9) The remainder for t+3 t+2 divided by 7 here would be 11 * 10 /7 REMAINDER 5
TWO VALUES FOR REMAINDERS JUST BY LOOKING AT 2 CASES DONT KNOW WHICH ONE STMT IS INSUFF TO ANSWER THE QUESTION
Building upon what was said above just as a double check....
(t+1) (t-1) = 7 (some integer)
Either t-1 is a multiple of 7 or t+1 is a multiple of 7
Lets say t+1 is a multiple of 7 ASSUME t=6
(t+1) (t-1) = 7 * 5 = 7 (some integer which is 5) The remainder for t+3 t+2 divided by 7 here would be 9 * 8 /7 REMIANDER 2
Lets say t-1 is a multiple of 7 ASSUME t=8
(t+1) (t-1) = 9 * 7 = 7 (some integer which is 9) The remainder for t+3 t+2 divided by 7 here would be 11 * 10 /7 REMAINDER 5
TWO VALUES FOR REMAINDERS JUST BY LOOKING AT 2 CASES DONT KNOW WHICH ONE STMT IS INSUFF TO ANSWER THE QUESTION
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Sorry for not being more specific.
OA's are official answers that you know are right for a given problem
SPOILER function (its one of the message body icons just below the subject) is just used to hide the OA so that we dont know the answer before we solve a problem (may also influence our thought process in solving the problem)
Eg: [spoiler]OA: whatever the correct choice is[/spoiler]
OA's are official answers that you know are right for a given problem
SPOILER function (its one of the message body icons just below the subject) is just used to hide the OA so that we dont know the answer before we solve a problem (may also influence our thought process in solving the problem)
Eg: [spoiler]OA: whatever the correct choice is[/spoiler]
Last edited by cramya on Fri Nov 14, 2008 6:30 pm, edited 1 time in total.
- logitech
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Beautifulcramya wrote:It is A and u did not miss D.
Building upon what was said above just as a double check....
(t+1) (t-1) = 7 (some integer)
Either t-1 is a multiple of 7 or t+1 is a multiple of 7
Lets say t+1 is a multiple of 7 ASSUME t=6
(t+1) (t-1) = 7 * 5 = 7 (some integer which is 5) The remainder for t+3 t+2 divided by 7 here would be 9 * 8 /7 REMIANDER 2
Lets say t-1 is a multiple of 7 ASSUME t=8
(t+1) (t-1) = 9 * 7 = 7 (some integer which is 9) The remainder for t+3 t+2 divided by 7 here would be 11 * 10 /7 REMAINDER 5
TWO VALUES FOR REMAINDERS JUST BY LOOKING AT 2 CASES DONT KNOW WHICH ONE STMT IS INSUFF TO ANSWER THE QUESTION
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"