oquiella wrote:The sum of the ages of Doris and Fred is y years. If Doris is 12 years older than Fred, how many years old will Fred be y years from now, in terms of y?
A. y - 6
B. 2y - 6
C. Y/2 - 6
D. 3Y/2 - 6
E. 5Y/2 - 6
Rich has demonstrate the input-output approach.
The algebraic approach is a little more complicated, but let's try it.
Doris is 12 years older than Fred. In other words, Doris' age = (Fred's age + 12).
So, the sum of their ages = (Fred's age) + (Fred's age + 12)
Simplify to get: sum of their ages = 2(Fred's age) + 12
We're told that the sum of the ages = y, so
2(Fred's age) + 12 = y
Now solve for Fred's age.
2(Fred's age) + 12 = y
2(Fred's age) = y - 12
Fred's age = (y - 12)/2
Fred's age = y/2 - 12/2
Fred's PRESENT age = y/2 - 6
How many years old will Fred be y years from now, in terms of y?
This equals
y/2 - 6 +
y
When we check the answer choices, we don't see
y/2 - 6 +
y, so we need to SIMPLIFY
y/2 - 6 +
y =
y/2 - 6 +
2y/2 (get common denominator of 2)
= 3y/2 - 6
=
D
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
