Derive as much information as you can out of the given data, and determine the value of n that will satisfy all the restraints.

Mo2men wrote:Mark and Ann together were allocated n boxes of cookies to sell for a club project. Mark sold 10 boxes less than n and Ann sold 2 boxes less than n. If Mark and Ann have each sold at least one box of cookies, but together they have sold less than n boxes, what is the value of n?

A) 11
B) 12
C) 13
D) 14
E) 15

We can PLUG IN THE ANSWERS, which represent the value of n.
When the correct answer choice is plugged in, the total sold will be less than n.

D: n=14
Since Mark sold 10 boxes less than n, the number sold by Mark = 14-10 = 4.
Since Ann sold 2 boxes less than n, the number sold by Ann = 14-2 = 12.
Total sold = 4+12 = 16.
Here, the total sold is GREATER THAN n.
Eliminate D.

B: n=12
Since Mark sold 10 boxes less than n, the number sold by Mark = 12-10 = 2.
Since Ann sold 2 boxes less than n, the number sold by Ann = 12-2 = 10.
Total sold = 2+10 = 12.
Here, the total sold is EQUAL TO n.
Eliminate B.

Notice the trend:
n=14 yields a sales volume GREATER THAN n.
n=12 yields a sales volume EQUAL TO n.
Implication:
A smaller value for n is required to yield a sales volume LESS THAN n.

The correct answer is A.

Algebraically:
Mark's sales = n-10.
Ann's sales = n-2.
Since the total sold must be less than n, we get:
(n-10) + (n-2) < n
2n-12 < n
n < 12.

The correct answer is A.

Mo2men wrote:Mark and Ann together were allocated n boxes of cookies to sell for a club project. Mark sold 10 boxes less than n and Ann sold 2 boxes less than n. If Mark and Ann have each sold at least one box of cookies, but together they have sold less than n boxes, what is the value of n?

A) 11
B) 12
C) 13
D) 14
E) 15

We are given that Mark sold 10 boxes less than n and Ann sold 2 boxes less than n, and that together they have sold less than n boxes. We can create the following inequality:

n - 10 + n - 2 < n

2n - 12 < n

n < 12

Answer: A