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Fred age

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Fred age

by deepoe » Thu May 21, 2009 3:52 am
The sum of the ages of Doris and Fred is Y years. If Doris is 12 years older than Fred, how many years will Fred be Y years from now, in term of Y?

A. y -6
B. 2y -6
C. (y/2) - 6
D. (3y/2) -6
E. (5y/2) -6


I picked numbers.

Sum of ages = 32

Doris = 22
Fred = 10

And than 10 years from now.

So Fred will be 22.

Answer is D, but i didn't got 22 as answer there.
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by scoobydooby » Thu May 21, 2009 4:20 am
notice the question asks y years from now.

y=sum of ages of Fed, Doris or 32 in your case.

fred in 32 years will be 10+32=42 yrs old

when you plug in the choices you get 42 only for choice D
for D, 3y/2-6=3*32/2-6=48-6=42
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by aj5105 » Thu May 21, 2009 4:23 am
D + F = Y

F + 12 + F = Y

Pick F = 10

(10 + 12) + 10 = 32

Y = 32

10 + 32 = 42 ( F, 32 years from now).

What you can do now is substitute Y = 32 in the answer choices. The one in which you get 42 is the answer.

(D)
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by bluementor » Thu May 21, 2009 4:31 am
you could try to solve this without plugging numbers:

Fred's age = F
Doris's age = D

F + Y = ?

Given that,

F + D = Y (eqn 1)

D = 12 + F (eqn 2)

(eqn 1) - (eqn 2):

F + D - D = Y - 12 - F
2F = Y - 12
2F + 2Y = Y - 12 + 2Y
2(F + Y) = 3Y - 12
F + Y = 3Y/2 - 6

Choose D.

-BM-
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by dhlee922 » Sun Jan 19, 2014 2:20 pm
never mind, i figured it out, need to add Y to both sides, which in effect cancels and you get the answers as stated above


why cant you say

1. D + F = Y
2. D = 12+F

from formulat 2 above, F = D-12

then to get Fred plus Y years, F = D - 12 + Y
D = Y - F from #1

F = Y - F -12 + Y
F = 2Y -F - 12
2F = 2Y - 12
F = Y -6
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