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# of books published

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# of books published

by LMK27 » Sat Apr 03, 2010 3:10 pm
What is the ratio of the number of books published by Publisher P in 1985 to the number of books published by Publisher P in 1990?

(1) Publisher P published 418,400 books in 1985 and 575,300 books in 1990.
(2) If the number of books published by Publisher P in 1985 was 10% greater, then it would be equal to 80% of the number of books that it published in 1990.

d
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Source: — Data Sufficiency |
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by LMK27 » Sat Apr 03, 2010 3:11 pm
Can someone pleaseee explain the easiest way to tackle #2?
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by Testluv » Sat Apr 03, 2010 3:53 pm
LMK27 wrote:Can someone pleaseee explain the easiest way to tackle #2?
....recognize that we can translate the sentence into an equation that would allow us to solve for 1985/1990:

(1.1)*(the number of books published in 1985) = (0.8)*(the number of books published in 1990)

We can rerrange this equation to solve for:

the number of books published in 1985/the number of books published in 1990

which is the ratio the question is asking for. Thus, the second statement is also sufficient.
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by LMK27 » Sat Apr 03, 2010 3:58 pm
Thanks. Can you explain a little further. I understand how you converted the statment but how do you figure out the # of books in 1985 and/or 1990? Since we can not use the information in part A, I am still a little confused on how translating the sentence actually is sufficient.
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by Testluv » Sat Apr 03, 2010 4:03 pm
LMK27 wrote:Thanks. Can you explain a little further. I understand how you converted the statment but how do you figure out the # of books in 1985 and/or 1990? Since we can not use the information in part A, I am still a little confused on how translating the sentence actually is sufficient.
We don't actually need to know the number of books.

If you have two unknowns, and you need to solve for either of them individually, then you need two equations.

BUT, if you have two unknowns, and you need to solve for some relationship between them (division, multiplication, addition, subtraction), then one equation will cut it.

For example:

What is the value of a + b?

(1) a + b = 10

Clearly, (1) is sufficient even though we don't know the actual values of "a" and "b". It could be 9 + 1 or 5 + 5 but either way (1) is sufficient.

That's what's going on in this problem (although the relationship is one of division rather than addition.)
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by LMK27 » Sat Apr 03, 2010 4:11 pm
Thanks for your explanation, I see what you mean now. DS is definitely my weakness!! :)
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