Bunuel
In a store, 40 items are arranged on a rack in 5 rows and 8 columns. The average (arithmetic mean) of the price of items in each row (m) is \(X_m\) [1 ≤ m ≤5]. The average of the price of items in each column (n) is \(Y_n\) [1 ≤ n ≤ 8]. What is the average price of all items on the rack?
(1) \(X_1 + X_2 + ... + X_5 = $850\)
(2) \(Y_1 + Y_2 + ... + Y_8 = $1,360\)
The average price of all items on the rack is the total sum of prices divided by the total number of items (40).
Average price of all items =
[ltr]

Total sum of prices/40[/ltr]
Let's evaluate the given statements:
(1) $X_1 + X_2 + \dots + X_5 = $850 From this statement, the sum of the average prices of each row is known.
The sum of the sums of prices in each row is
[ltr]

8×(X1+X2+...+X5)=8×850=6800[/ltr]
.
The total sum of prices of all 40 items is 6800.
The average price of all items =
[ltr]

6800/40=170[/ltr]
.
Therefore, statement (1) alone is sufficient to find the average price of all items.
(2) $Y_1 + Y_2 + \dots + Y_8 = $1,360 From this statement, the sum of the average prices of each column is known.
The sum of the sums of prices in each column is
[ltr]

5×(Y1+Y2+...+Y8)=5×1360=6800[/ltr]
.
The total sum of prices of all 40 items is 6800.
The average price of all items =
[ltr]

6800/40=170[/ltr]
.
Therefore, statement (2) alone is also sufficient to find the average price of all items.
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