Linear equation Word Problem

Question

Marylins age in 15 years will be twice what it was 7 years ago. How old is Marylin now

Answer 1

To start out, let A = Marylin's age now and A - 7 = her age 7 years ago.  We are then told that  A + 15 = 2(A -7).

 

 Expanding the equation  we get A + 15 = 2A - 14.  Putting the A's on one side of the equation we get

 

15 + 14 = 2A - A.   Combining terms, we get A = 29.  Marylin is now 29 years old.

 

To test this answer 29 + 15 = 44 and 29 - 7 = 22.  Indeed, 44 is twice 22.

 

I hope this helps.  Please contact me if you would like regular tutoring.  I am also available for online tutoring.

 

All the best,

 

Thomas

Answer 2

Let m=Marylin's age now

 

"Marylin's age in 15 years" is shown by m+15

"twice what it was 7 years ago" is shown by 2(m-7)

m-7 is her age 7 years ago. So, 2 times (m-7) is "twice" what her age was 7 years ago.

 

To show "Marylins age in 15 years will be twice what it was 7 years ago," we just set these two expressions equal to each other.

 

  m+15=2(m-7)    Now we solve for m

  m+15=2m-14

-2m      -2m

 -m+15=-14

      -15  -15

       -m=-29

        m=29

 

Let's see if it's true. If Marylin is 29 now, in 15 years she'll be 44. If Marylin is 29 now, then 7 years ago she was 22. Is 44 twice 22? Yes it is. Alternatively, you could substitute m=29 into the equation to check the accuracy.

Answer 3

Allow x to represent Marylin's current age in years. This will be the point of reference upon which you will build the rest of the equation.

 

Her age 15 years from now would be represented by the phrase (x+15).

The result of (x+15) is equal to TWICE the age she was 7 years ago, or 2(x-7).

 

So, (x+15)=2(x-7)

 

Solve for x.

 

Regards.