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If John brought n comic books at $2 each, then brought m comic books

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Bunuel
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If John brought n comic books at $2 each, then brought m comic books [#permalink] New post   28 Dec 2017, 00:10
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If John brought n comic books at $2 each, then brought m comic books at $7 each, and m- n comic books at $13 each, then the average (arithmetic mean) cost, in dollars per comic book, is equal to

A. 22(m + n)/m

B. (20m - 11n)/(2m)

C. 11m

D. (6m - 15n)/(2m - 2n)

E. 22mn/(m + n)
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DavidTutorexamPAL
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Re: If John brought n comic books at $2 each, then brought m comic books [#permalink] New post   28 Dec 2017, 03:56
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Bunuel wrote:
If John brought n comic books at $2 each, then brought m comic books at $7 each, and m- n comic books at $13 each, then the average (arithmetic mean) cost, in dollars per comic book, is equal to

A. 22(m + n)/m

B. (22m - 11n)/(2m)

C. 11m

D. (6m - 15n)/(2m - 2n)

E. 22mn/(m + n)


As all our values are small, we'll go for a straightforward calculation.
This is a Precise approach.

Total money spent is n*2 + m*7 + (m-n)*13 = m*20 - n*11
Total comic books purchased = n + m + (m-n) = 2m
Average price per book is (m*20 - n*11)/2m.

Bunuel are you sure the question is correct? If I'm not mistaken the coefficient of m should be 20 and not 22 in all relevant answers. (Or the question stem should be different)
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Bunuel
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Re: If John brought n comic books at $2 each, then brought m comic books [#permalink] New post   28 Dec 2017, 04:06
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DavidTutorexamPAL wrote:
Bunuel wrote:
If John brought n comic books at $2 each, then brought m comic books at $7 each, and m- n comic books at $13 each, then the average (arithmetic mean) cost, in dollars per comic book, is equal to

A. 22(m + n)/m

B. (22m - 11n)/(2m)

C. 11m

D. (6m - 15n)/(2m - 2n)

E. 22mn/(m + n)


As all our values are small, we'll go for a straightforward calculation.
This is a Precise approach.

Total money spent is n*2 + m*7 + (m-n)*13 = m*20 - n*11
Total comic books purchased = n + m + (m-n) = 2m
Average price per book is (m*20 - n*11)/2m.

Bunuel are you sure the question is correct? If I'm not mistaken the coefficient of m should be 20 and not 22 in all relevant answers. (Or the question stem should be different)


My mistake, you are right. Edited. Thank you.
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Re: If John brought n comic books at $2 each, then brought m comic books [#permalink] New post   28 Dec 2017, 09:30
Bunuel wrote:
If John brought n comic books at $2 each, then brought m comic books at $7 each, and m- n comic books at $13 each, then the average (arithmetic mean) cost, in dollars per comic book, is equal to

A. 22(m + n)/m

B. (20m - 11n)/(2m)

C. 11m

D. (6m - 15n)/(2m - 2n)

E. 22mn/(m + n)


\(\frac{2n + 7m + 13m - 13n}{m + n + m - n}\)

Or, \(\frac{20m - 11n}{2m}\), answer will be (B)
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Re: If John brought n comic books at $2 each, then brought m comic books [#permalink]
28 Dec 2017, 09:30
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