BTGModeratorVI wrote: ↑Sat Aug 08, 2020 7:13 am
If x is a positive number less than 10, is z greater than the average (arithmetic mean) of x and 10?
(1) On the number line, z is closer to 10 than it is to x.
(2) z = 5x
Answer:
A
Source: Official guide
Target question: Is z greater than the mean of x and 10?
Statement 1: On the number line, z is closer to 10 than it is to x.
IMPORTANT: On the number line, the mean of two numbers will lie at the
midpoint between those two numbers.
So, the mean of x and 10 will lie
halfway between x and 10.
So, if z is closer to 10 than it is to x, then
z must lie to the right of the midpoint between x and 10.
This means that
z must be greater than the mean of x and 10
Since we can answer the
target question with certainty, statement 1 is SUFFICIENT
Statement 2: z = 5x
There are several pairs of numbers that meet this condition. Here are two:
Case a: x=1, z=5, in which case
z is less than the mean of x and 10 (mean = 5.5)
Case b: x=4, z=20, in which case
z is greater than the mean of x and 10 (mean = 7)
Since we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Answer: A
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
