BTGModeratorVI wrote: ↑Mon Sep 14, 2020 8:35 am
The people in a line waiting to buy tickets to a show are standing one behind the other. Adam and Beth are among the people in the line, and Beth is standing behind Adam with a number of people between them. If the number of people in front of Adam plus the number of people behind Beth is 18, how many people in the line are behind Beth?
(1) There are a total of 32 people in the line.
(2) 23 people in the line are behind Adam.
Answer:
C
Source: Official guide
Target question: How many people in the line are behind Beth?
Given: Beth is standing behind Adam with a number of people between them. The number of people in front of Adam plus the number of people behind Beth is 18
So, we have: FRONT.....x people...ADAM......y people.....BETH......z people......BACK
We can write:
x + z = 18
NOTE: Our goal is to determine
the value of z
Statement 1: There are a total of 32 people in the line
We can write: x + y + z + 2 = 32 (the 2 represents Adam and Beth)
Simplify: x + y + z = 30
Is this information, along with
x + z = 18, enough to determine the
value of z?
No. There are several values of x, y and z that satisfy statement 1. Here are two:
Case a: x = 1, y = 12 and z = 17. In this case,
z = 17
Case b: x = 2, y = 12 and z = 16. In this case,
z = 16
Since we cannot answer the
target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: 23 people in the line are behind Adam
We can write: y + z + 1 = 23 (the 1 represents Beth)
Simplify: y + z = 22
Is this information, along with
x + z = 18, enough to determine the
value of z?
No. There are several values of x, y and z that satisfy statement 1. Here are two:
Case a: x = 2, y = 6 and z = 16. In this case,
z = 16
Case b: x = 3, y = 7 and z = 15. In this case,
z = 15
Since we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Statements 1 and 2 combined
Statement 1 tells us that x + y + z = 30
Statement 2 tells us that y + z = 22
Plus, it's given that
x + z = 18
Since we have three different equations with 3 variables, we COULD solve this system for x, y and z, which means we COULD determine
the value of z (the number of people behind Beth) . Of course, we're not going to waste valuable time solving the system, since our sole goal is to determine the sufficiency of the statements.
Since we can answer the
target question with certainty, the combined statements are SUFFICIENT
Answer: C
Cheers,
Brent
