Data Sufficiency

The cost of delivery for an order of desk chairs was $10.00 for the first chair and $1.00 for each additional chair in the order. If an office manager placed an order for \(n\) desk chairs, is \(n > 24 ?\)

(1) The delivery cost for the order totaled more than $30.00.
(2) The average (arithmetic mean) delivery cost of the \(n\) chairs was $1.36.

[spoiler]OA=B[/spoiler]

Source: GMAT Prep

Using (1), the total is to be more than $30, which can be the case if n is greater than or less than 24. For instance, when n=22, the total cost is $31, but when n=25, the total cost is $34, which are both greater than $30. Insufficient.

Using (2), we are given that [10 + (n-1)]/n = 1.36

=> n= 25, which is greater than 24. Sufficient.

Answer B.