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) \(Y_1 + Y_2 + ... + Y_8 = $1,360\)
Since there are 8 columns, therefore each of the 5 rows will have 8 items (A quick diagram of the setup will help)
Similarly, each column will have 5 items.
Statement 1:
If we multiply the average of the row \(X_1\) with the number of items in the row, which is 8, we would get the sum of the items in row 1.
Doing the same for the other rows and adding all together would give the sum of all the 40 items:
\(8X_1 + 8X_2 + ... + 8X_5 = 8(X_1 + X_2 + ... + X_5)= $8*850\)
Similarly for statement 2:
we can multiply the number of items in a column, which is 5, with the average of the column \(Y_1\) to get the sum of the items in the column
\(5Y_1 + 5Y_2 + ... + 5Y_8= 5(Y_1 + Y_2 + ... + Y_8)= $5*1,360\)
Therefore, D.