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Re: Jack is now 14 years older than Bill. If in 10 years Jack [#permalink]

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10 Jan 2014, 02:57

1

This post was BOOKMARKED

Walkabout wrote:

Jack is now 14 years older than Bill. If in 10 years Jack will be twice as old as Bill, how old will Jack be in 5 years?

(A) 9 (B) 19 (C) 21 (D) 23 (E) 33

Set up the equations: [J = B + 14] and [J + 10 = 2(B + 10)], subtract the two and solve for B, this gives us B = 4.. From the first equation we know that Jack is 14 years older than Bill today, which means that Jack is 14 + 4 = 18 years old.. So naturally, in 5 years he's 23 years old.

Jack is now 14 years older than Bill. If in 10 years Jack will be twice as old as Bill, how old will Jack be in 5 years?

(A) 9 (B) 19 (C) 21 (D) 23 (E) 33

Currently: J = B + 14; In 10 year: J + 10 = 2(B + 10);

Solving gives J = 18;

Thus in 5 years Jack will be 18 + 5 = 23 years old.

Answer: D.

We know that J = B + 14

B = J + 14

So to add 10 to both sides, we get

J + 10 = 2 ( B + 14 ) + 10

Why should we have 2 ( B + 10 ) ?

Thanks,

First of all, from J = B + 14, we get that B = J - 14, not B = J + 14.

Next, we are told that in 10 years Jack will be twice as old as Bill: in 10 years, Jack will J + 10 years and Bill will be B + 10 years. So, J + 10 = 2(B + 10).

Re: Jack is now 14 years older than Bill. If in 10 years Jack [#permalink]

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15 Jul 2014, 12:09

I did this using number substitution. When we set up J=B+14, and we want to know J+5, we can safely say we want B+19 here. Since B cannot be zero, a and b are ruled out. Then you substitute the remaining values, starting from the middle one, which is 23. And you get the answer.

Re: Jack is now 14 years older than Bill. If in 10 years Jack [#permalink]

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14 Jun 2015, 17:28

Thinking out the problem conceptually you can solve the problem quite quickly in your head(or paper):

1) If Jack is twice as old as Bill in 10 years then the difference between the two ages(at that time) is equal to Bill's age! Since they are 14 years apart (always), Bill is currently 4 and Jack 18. 2)18+5 = 23 -->(D)

Jack is now 14 years older than Bill. If in 10 years Jack will be twice as old as Bill, how old will Jack be in 5 years?

(A) 9 (B) 19 (C) 21 (D) 23 (E) 33

We first want to create variables for Jack’s age today and Bill’s age today.

J =Jack’s age today

B = Bill’s age today

Now we can use these variables to set up two equations.

We are given that Jack is now 14 years older than Bill. This relationship is represented in our first equation.

J = B + 14 Eq (1)

Next we are given that in 10 years Jack will be twice as old as Bill. Remember, in setting up this equation we must add 10 years to both Jack's and Bill’s current ages, respectively.

10 + J = 2(B + 10)

10 + J = 2B + 20

J = 2B + 10 Eq (2)

Now we can set our two equations (Eq (1) and Eq (2)) equal to each other and determine the value of B.

B + 14 = 2B + 10

B = 4

This means that Bill’s age today is 4.

Thus, we know that Jack’s age today is 14 + 4 = 18.

This means that Jack’s age in 5 years will be 18 + 5 = 23.

Answer is D
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