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# Last year the average (arithmetic mean) of monthly cookie sales triple

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Math Expert
Joined: 02 Sep 2009
Posts: 58465
Last year the average (arithmetic mean) of monthly cookie sales triple  [#permalink]

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09 Jan 2018, 05:32
00:00

Difficulty:

45% (medium)

Question Stats:

64% (01:53) correct 36% (02:01) wrong based on 30 sessions

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Last year the average (arithmetic mean) of monthly cookie sales tripled each quarter from the per month average from the previous quarter. If the average for the first quarter's cookie sales was z, what were the total cookie sales for the year in terms of z?

A. 30z
B. 40z
C. 120z
D. 140z
E. 160z

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Joined: 22 Nov 2017
Posts: 25
Location: United States
Concentration: Technology, Healthcare
Re: Last year the average (arithmetic mean) of monthly cookie sales triple  [#permalink]

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09 Jan 2018, 06:03
1
First quarter average is z. So sum of first 3 month sales is (m1 +m2 + m3) = 3z. Next quarter monthly sales becomes 3 times earlier quarter. So m4 + m5 + m6 = 3 x 3z is 9z. Similarly quarter 3 sum becomes 27z and last quarter sum becomes 81z. So full year total sales is 3z + 9Z + 27z + 81z = 120z. Answer is C.

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Re: Last year the average (arithmetic mean) of monthly cookie sales triple   [#permalink] 09 Jan 2018, 06:03
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