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Bunuel
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Nidzo
\( a = b + 1\)

Rate of machine A: \(\frac{1}{b+1}\)

Rate of machine B: \(\frac{1}{b}\)


Combined rate: as they do 90% of p in 2 hours the rate becomes-

\(\frac{1}{b+1} + \frac{1}{b} = \frac{\frac{9}{10}}{2}\)


\(\frac{2b+1}{b^2+b} = \frac{9}{20}\)

\(40b + 20 = 9b^2 + 9b \)

\(9b^2 - 31b - 20 = 0\)

\((9b + 5)(b - 4)\)

b = \(\frac{5}{9}\) or b = \(4\)

Answer can only be 4, so B.
can you pls tell how you solved this part 9b^2 - 31b - 20 = 0 since this equation till this point was as it is time consuming
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9p/10 page printed in 2 hours.
Then p pages are printed by both printers in 20/9 hours.

1/rate of A + 1/rate of B = 9/20
AS A takes one hour longer, it can be 5 and 4. Because 1/5+1/4 =9/20

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Bunuel
Two printing presses, press A and press B, working together at their respective constant rates, can print 9p/10 pages in 2 hours. If press A takes 1 hour longer than press B to print p pages, how many hours does it take press B to print p pages?

A. 3
B. 4
C. 5
D. 6
E. 7

Together they can print 9p/10 pages in 2 hrs.
So they can print p pages in 2 * 10/9 = 20/9 hrs
B can print p pages in B hrs
A can print p pages in B+1 hrs

Combined rate = 9/20
Rate of B = 1/B
Rate of A = 1/(B+1)

\(\frac{1}{B} + \frac{1}{(B+1)} = \frac{9}{20}\)

We need 20 in the denominator and B and B+1 are consecutive integers. We know that they could be 4 and 5. Let's check.

\(\frac{1}{4} + \frac{1}{5} = \frac{9}{20}\) - Valid

Hence B takes 4 hrs to print p pages.

Answer (B)
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