Suppose (b_a)^2=71_a, where a and b represent two distinct digits. If b=a-1, find a.

 Jun 15, 2018

If the underscore is supposed to be a minus sign then, 

Since b = a-1, we can substitute the b in the first equation with a-1.
Then, we solve for a.

\((b-a)^2=71-a\\ (a-1-a)^2=71-a\\ (-1)^2=71-a\\ 1=71-a\\ a=70\)

 Jun 15, 2018

Melody: This answer was posted by either "Gavin" or by "ChowMein", because I saw one of their names on it originally, but later, for some reason, they changed it to "Guest". You may query them privately to confirm this fact. Thank you.

Guest Jun 17, 2018

OMG! Melody! How could you give this post a point and a CHECK mark?

This is like rating a bond in default as “AA”


Mr. BB’s interpretation is not just a blarney banker interpretation; it is blatant bullshit! 


 The (a) and (b) are digits of a number.  For (71_a), (a) is the final digit.


There a minus sign used in the question, so the asker is not confused about it. 


I recall someone describing a kangaroo as a large mouse. That was quite funny. This isn’t!


Related post:  https://web2.0calc.com/questions/what-is-the-sum-of-the-odd-numbers-from-1-to-387#r1





 Jun 15, 2018

To be honest Ginger I did not, and still have not, looked at the answer.

I don't have the time. So mostly these days I give points for 'perceived' effort.


As for the check mark, well the poster can jump up and down and ask for another answer. 

Or if they are polite they can just question the answer.


99% of them do not care enough to do so. Until someone complains I suppose I figure that an answer is an answer.

If they are wrong sometimes it might discourage the student from having blind faith in this forum as a means of cheating.


I know there are exceptions but it seems to me that if a asker is really interested in learning they will be a member and they will become known to us in order to increase our desire to help them.

Melody  Jun 15, 2018

Actually the answer is not bad Ginger.

The answerer mistook the symbol for a minus sign. That is not unreasonable at all.

Am I missing something ?

Melody  Jun 16, 2018

If this were some young student on here, I’d agree that it’s reasonable.

Mr. BB isn’t a young student; he’s an old Blarney Bag who throws BS at questions until some of it sticks.  Mr. BB didn’t mistake the symbol for a minus sign; he’s not that blind, and there is a properly used minus sign in the question, so it’s unlikely the asker confused the two symbols.


Mr. BB chose to use it because he understands the function and it gives “a solution.” 

He’s continued to throw BS on it–on this thread and here, where he created another post with the same question.   

For the psychology behind this behavior, see this:  https://web2.0calc.com/questions/what-is-the-sum-of-the-odd-numbers-from-1-to-387#r2


I’ve seen these types of questions on GMAT forums.

This question, as asked, has no solution.


Here’s a list of squares of concatenated numbers (b_a)


b   a    concatenated  square

0    1         1                    1
1    2        12               144
2    3        23               529
3    4        34             1156
4    5        45             2025
5    6        56             3136
6    7        67             4489
7    8        78             6084
8    9        89             7921



45 and 56 have squares where the (a) digit is the final digit of the square, but this is not in the form of (71a). 



Mr. BB seems like a phage on this forum, but I suppose in the scheme of things, that Mr. BB’s posts are just weeds, with annoying flies, in the gardens of Camelot. The students will have to learn to recognize them and treat them accordingly.   


GETSMART is looking forward to Thanksgiving. The poor turkey is hoping someone will eat him and put him out of his misery.indecision



GingerAle  Jun 16, 2018

I think the question is about 2 numbers a, b in other bases. For example: 8^2 in base 9 =71 in base 9.

Since it says: b=a - 1, then since b=8 and a =9, then b=9 - 1=8, which agrees with above.

 Jun 16, 2018

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