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A total of 20 amounts are entered on a spreadsheet that has

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A total of 20 amounts are entered on a spreadsheet that has [#permalink]

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A total of 20 amounts are entered on a spreadsheet that has 5 rows and 4 columns; each of the 20 positions in the spreadsheet contains one amount. The average (arithmetic mean) of the amounts in row (i) is R(i) (1≤(i)≤5). The average of the amounts in column (j) is C(j) (1≤(j)≤4). What is the average of all 20 amounts on the spreadsheet?

(1) R1 + R2 + R3 + R4 + R5 = 550
(2) C1 + C2 + C3 + C4 = 440
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Re: What is the average of all 20 amounts on the spreadsheet? [#permalink]

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New post 02 Mar 2012, 03:11
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A total of 20 amounts are entered on a spreadsheet that has 5 rows and 4 columns; each of the 20 positions in the spreadsheet contains one amount. The average (arithmetic mean) of the amounts in row (i) is R(i) (1≤(i)≤5). The average of the amounts in column (j) is C(j) (1≤(j)≤4). What is the average of all 20 amounts on the spreadsheet?

X--X--X--X --> R1
X--X--X--X --> R2
X--X--X--X --> R3
X--X--X--X --> R4
X--X--X--X --> R5
__________
C1-C2-C3-C4

(1) R1 + R2 + R3 + R4 + R5 = 550 --> since R1 is the average of row 1, then the sum of the numbers in row 1 is R1*4, the sum of the numbers in row 2 is R2*4, and so on. Hence the sum of all 20 numbers is 4*(R1 + R2 + R3 + R4 + R5)=4*550 --> the average of all 20 numbers is (average)=(sum)/(# of terms)=(4*550)/20=110. Sufficient.

(2) C1 + C2 + C3 + C4 = 440. The same logic here: the sum of the numbers in column 1 is C1*5, the sum of the numbers in column 2 is C2*5, and so on. Hence the sum of all 20 numbers is 5*(C1 + C2 + C3 + C4 )=5*440 --> the average of all 20 numbers is (average)=(sum)/(# of terms)=(5*440)/20=110. Sufficient.

Answer: D.

Hope it's clear.
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Re: A total of 20 amounts are entered on a spreadsheet that has [#permalink]

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New post 10 Apr 2017, 08:28
A total of 20 amounts are entered on a spreadsheet that has 5 rows and 4 columns; each of the 20 positions in the spreadsheet contains one amount. The average (arithmetic mean) of the amounts in row (i) is R(i) (1≤(i)≤5). The average of the amounts in column (j) is C(j) (1≤(j)≤4). What is the average of all 20 amounts on the spreadsheet?

(1) R1 + R2 + R3 + R4 + R5 = 550
divide by 5. suff.
(2) C1 + C2 + C3 + C4 = 440
divide by 4.
suff.

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Re: A total of 20 amounts are entered on a spreadsheet that has [#permalink]

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New post 10 Apr 2017, 13:45
Yeah it definetely does not feel like a sub-600 question. But apart from being a bit abstract it doesn't require any calculations, just a certain level of reasoning. Both I and II are valid since both give you the sum of either the rows or columns, which allows us to calculate the the average.
Re: A total of 20 amounts are entered on a spreadsheet that has   [#permalink] 10 Apr 2017, 13:45
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