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Same method not working in 2 age problems

  1. Oct 5, 2017 #1
    1. The problem statement, all variables and given/known data

    Q1. Lindsay is twice as old as she was 10 years ago. Kimberly is half as old as she will be in 10 years.

    Find Lindsay’s age now?

    Find Kimberly’s age now?

    Q2.
    In 8 years Tiffany will be 3 times as old as she is now. The number of years until Tiffany will be 6 times as old as she is now.
    2. Relevant equations
    Simple algebric equation of one variable

    3. The attempt at a solution
    Q1 Solution:
    Let L = Lindsay’s age & K = Kimberly’s age

    L=2(L-10)=>L=20

    K=1/2(K+10)=>k=10

    Q2 Solution:
    T = 3(T+8)

    But this is not correct. Some body guide me. The wordings of two questions are same but why same technique not working.


    Zulfi.
     
  2. jcsd
  3. Oct 5, 2017 #2

    haruspex

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    How are you defining T here? Age now?
     
  4. Oct 5, 2017 #3

    Mark44

    Staff: Mentor

    Because your equation is wrong.
    Your equation says that Tiffany's age now is equal to 3 times her age in 8 years. That can't be true. People's ages normally get larger, not smaller.
     
  5. Oct 10, 2017 #4
    Hi,

    I am able to find out the correct equation. The correct equation is:

    T+8 = 3T

    The complete question is:

    In 8 years Tiffany will be 3 times as old as she is now. The number of years until Tiffany will be 6 times as old as she is now. Find out the number of years until Tiffany will be 6 times as old as she is now.


    My solution is:

    T+8 = 3T =>2T = 8 => T =4

    6 times = 6 * 4= 24

    Therefore number of years until Tiffany will be 6 times as old as she is now = 24-20 =20

    Please tell me if its right or wrong.


    Zulfi.
     
  6. Oct 10, 2017 #5

    haruspex

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    It's right.
     
  7. Oct 11, 2017 #6

    Mark44

    Staff: Mentor

    So, in the language of the problem, Tiffany's age right now is 4.
    There's no need to ask us to confirm whether your answer is correct or not. You should get in the habit of checking your answers. If you start out by defining your variables clearly, then it makes it easier to write correct equations as well as to check your solutions.

    In this problem, Tiffany's age now is 4. How old will she be in 8 years? Will her age then be three times her age now? In 20 years how old will she be? Will her age by six times what it is now?
     
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