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Ten years ago, the average age of a couple was 27 years old. Today

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cfc198
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Ten years ago, the average age of a couple was 27 years old. Today [#permalink] New post   07 Jan 2019, 11:06
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Ten years ago, the average age of a couple was 27 years old. Today also the average age of the couple and their baby is 27 years old. Find the present age of the baby.

A 4
B 3
C 2
D 5
E 7
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E
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Ten years ago, the average age of a couple was 27 years old. Today [#permalink] New post   07 Jan 2019, 11:30
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cfc198 wrote:
Ten years ago, the average age of a couple was 27 years old. Today also the average age of the couple and their baby is 27 years old. Find the present age of the baby.

A 4
B 3
C 2
D 5
E 7


Couple's age = x+y, Baby's age = z

Ten years Ago,
\(\frac{x+y}{2}\)- 10 =27
x+y-20 = 54
x+y =74

\(\frac{x+y+z}{3}\) =27
x+y+z = 81
z = 7

Correct Answer E
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Re: Ten years ago, the average age of a couple was 27 years old. Today [#permalink] New post   09 Jan 2019, 02:02
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cfc198 wrote:
Ten years ago, the average age of a couple was 27 years old. Today also the average age of the couple and their baby is 27 years old. Find the present age of the baby.

A 4
B 3
C 2
D 5
E 7


Couple's age = x+y, Baby's age = z

Ten years Ago,
x+y =27 * 2
x+y= 54

after 10 years

(x+10)+(y+10)+z =27 * 3
x+y+z = 81
z = 7

Correct Answer E
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Re: Ten years ago, the average age of a couple was 27 years old. Today [#permalink] New post   09 Jan 2019, 11:44
Sum of age of parents,10 years ago= 27*2=54
Therefore, some of age of parents today= 54+10+10 =74 (adding 10 years to the age of both of the parent)
But today, age of parents and child average to 27 years.
So, sum of the ages of the three,today=27*3=81
Thus, age of child= age of all three-age of parents= 81-74=7

Hence, E
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Ten years ago, the average age of a couple was 27 years old. Today [#permalink] New post   09 Jan 2019, 22:20
Expert Reply
cfc198 wrote:
Ten years ago, the average age of a couple was 27 years old. Today also the average age of the couple and their baby is 27 years old. Find the present age of the baby.

A 4
B 3
C 2
D 5
E 7


Use the concept of deviation to solve it in seconds.

Th average age of two people was 27 so they were effectively 27 years old each.
After 10 yrs, there was an extra 20 yrs deviation but average remained same so there must have been a shortfall of 20 too. The shortfall would come from the child's age so the child must be 27 - 20 = 7 years old.

Answer (E)
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Ten years ago, the average age of a couple was 27 years old. Today [#permalink]
09 Jan 2019, 22:20
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