2012 AMC 10B Problems/Problem 6
Problem 6
In order to estimate the value of 
where 
and 
are real numbers with 
, Xiaoli rounded up by a small amount, rounded down by the same amount, and then subtracted her rounded values. Which of the following statements is necessarily correct?
A) Her estimate is larger than
B) Her estimate is smaller than
C) Her estimate equals
D) Her estimate equals 
E) Her estimate is 
Solutions
Say Z=is the amount rounded up by and down by.
Xiaoli rounded x up by a small amount, rounded y down by the same amount, and then subtracted her rounded values.
Which translates to:
=
=
This is 
bigger than the original amount of 
.
Therefore, her estimate is larger than
or
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions. 
