swerve wrote:The price of a phone call consists of a standard connection fee, which is constant, plus a per minute charge. A 10-minute call costs $2.90 and a 16-minute call costs $4.40. How much does a 13-minute call cost?
A. $3.55
B. $3.57
C. $3.58
D. $3.65
E. $3.77
The OA is D
Source: Manhattan Prep
Let C = price of connection fee
Let M = the price PER MINUTE
A 10-minute call costs $2.90
We can write:
C + 10M = 2.90
A 16-minute call costs $4.40.
We can write:
C + 16M = 4.40
How much does a 13-minute call cost?
So far, we have:
C + 10M = 2.90
C + 16M = 4.40
ONE (
slower) approach would be to solve the system for C and M, and then calculate the cost of a 13-minute call.
The
FASTER approach is to recognize that something great happens when we
ADD the two equations
We get: 2C + 26M = 7.30
Now divide both sides by 2 to get: C + 13M = 3.65
Since C + 13M represents the TOTAL cost of a 13-minute call, we can conclude that a 13-minute call costs $3.65
Answer: D
Cheers,
Brent
