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Bunuel

Can you please clearify all shelves but the last one contained 8 books and that last shelf contained 11 books a bit more, because it is very confusing to me.

What is it that the above statement is trying to convey?

Does the it say that all the shelves contains 8 books and the last one 11 books after the rearrangement of course, meaning 12X-21?

Yes or No?

I have really no idea what this question is talking about, because of the above statement.

Please your help and clarification.

Thanks in advance!
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Bunuel

Can you please clearify all shelves but the last one contained 8 books and that last shelf contained 11 books a bit more, because it is very confusing to me.

What is it that the above statement is trying to convey?

Does the it say that all the shelves contains 8 books and the last one 11 books after the rearrangement of course, meaning 12X-21?

Yes or No?

I have really no idea what this question is talking about, because of the above statement.

Please your help and clarification.

Thanks in advance!
­
After rearrangement, all except the last one have 8 books each, and the last shelf has 11 books. 
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­where it is mentioned as 8 books each shelf?????

each is missing. statement is not clear itself
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Happysumit007
­where it is mentioned as 8 books each shelf?????

each is missing. statement is not clear itself
To uinderstand you should read carefully:
­

Each shelf of a bookcase contained 12 books. If the librarian took out 21 books and rearranged the remaining books so that all shelves but the last one contained 8 books and that last shelf contained 11 books, how many shelves does the bookcase have?­
The highlighted part means that after rearrangement, all except the last one have 8 books each, and the last shelf has 11 books.­
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another way to solve this incase it doesn't click that RHS will have x - 1 shelves:

x shelves, each contain 12 books so total 12x books

he removed 21 books so remaining books = 12x - 21

above was arranged such that all shelves but the last one contained 8 books and that last shelf contained 11 books: 8q + 11
here q is the number of shelves (technically its x-1 but incase that doesn't click then based on this info we can equate it to a 'multiple of 8 + 11 books')

so final equation becomes:

12x - 21 = 8q + 11
-> 12x = 8q + 32
reducing: 3x = 2q+8
now look at the options, 6 fits! [ 3 * 6 = 2 * 5 + 8]
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average time people took for this was 2 mins 50 secs. i solved it in 45secs.
very simply-
there were 12 books per shelf & now it was down to 8. that's a difference of 4. & 21 were removed- so 4*5=20. & the one remaining was from the last shelf-> hence it had 11 books. This makes it a total of 6 shelves.
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I solved in a simpler way (unsure right or wrong)
4 books from each shelf is removed and 1 from last.
so, 21 (Total books) = 4 * X + 1
it gives X as 5 (+1 for last shelf) = 6
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I like the solution - it’s helpful. I did 12x-21 = 8x + 11 and got 8, but I see where I went wrong.
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Hi,

I think the issue here is that instead of x, it should be x-1 since its 8 books/shelf except the last one. If you solve using this method, you will get to the right answer i.e. 6
Fisayofalana
I like the solution - it’s helpful. I did 12x-21 = 8x + 11 and got 8, but I see where I went wrong.
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Deconstructing the Question
Initially, each shelf has \(12\) books. If there are \(s\) shelves, total books are \(12s\).
After removing \(21\) books, remaining books are \(12s-21\).
After rearranging: all but the last shelf have \(8\) books, and the last shelf has \(11\) books.
So the rearranged total is \(8(s-1)+11\).

Step-by-step
Set remaining books equal to rearranged books:
\(12s-21=8(s-1)+11\)

Simplify:
\(12s-21=8s-8+11\)
\(12s-21=8s+3\)
\(4s=24\)
\(s=6\)

Answer: 6
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