SOLUTION: Hi there, I was given the following problem and I just can't figure it out. Could you please let me know how to come up with the answer? Thanks! Given these facts: Jack's age

Algebra ->  Equations -> SOLUTION: Hi there, I was given the following problem and I just can't figure it out. Could you please let me know how to come up with the answer? Thanks! Given these facts: Jack's age      Log On


   



Question 1036524: Hi there,
I was given the following problem and I just can't figure it out. Could you please let me know how to come up with the answer? Thanks!
Given these facts: Jack's age plus Marie's age is 27; Jack's age plus Fred's age is 38; Marie's age plus Fred's age is 33. How old is Jack?

Found 3 solutions by josgarithmetic, MathTherapy, ikleyn:
Answer by josgarithmetic(39616) About Me  (Show Source):
You can put this solution on YOUR website!
.
Hi there,
I was given the following problem and I just can't figure it out. Could you please let me know how to come up with the answer? Thanks!
Given these facts: Jack's age plus Marie's age is 27; Jack's age plus Fred's age is 38; Marie's age plus Fred's age is 33. How old is Jack?
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j, m, f their ages. Then
system%28j+%2B+m+=+27%2C%0D%0Aj+%2B+f+=+38%2C%0D%0Am+%2B+f+=+33%29


Answer by MathTherapy(10551) About Me  (Show Source):
You can put this solution on YOUR website!

Hi there,
I was given the following problem and I just can't figure it out. Could you please let me know how to come up with the answer? Thanks!
Given these facts: Jack's age plus Marie's age is 27; Jack's age plus Fred's age is 38; Marie's age plus Fred's age is 33. How old is Jack?
Let Jack's age, be J
Then Marie's is: 27 - J, and Fred's is: 38 - J
Also, 27 - J + 38 - J = 33
- J - J + 65 = 33
- J - J = 33 - 65
- 2J = - 32
J, or Jack's age is = %28-+32%29%2F%28-+2%29, or highlight_green%2816%29

Answer by ikleyn(52776) About Me  (Show Source):
You can put this solution on YOUR website!
.
Hi there,
I was given the following problem and I just can't figure it out. Could you please let me know how to come up with the answer? Thanks!

Given these facts: Jack's age plus Marie's age is 27; Jack's age plus Fred's age is 38; Marie's age plus Fred's age is 33. How old is Jack?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Let j, m, f be their ages.  Then

j + m = 27,    (1)
j + f = 38,    (2)
m + f = 33.    (3)

The method to solve this system is as follows.

Add equations (1), (2) and (3) (both left sides and right sides). You will get

2*(j + m + f) = 27 + 38 + 33 = 98,   or

j + m + f = 49.    (4)     ( <<<--- 49 = 98%2F2 )

Now, distract equation (1) from (4). You will get

f = 49 - 27 = 22.

Next, distract equation (2) from (4). You will get

m = 49 - 38 = 11.

Finally, distract equation (3) from (4). You will get

j = 49 - 33 = 16.

Answer.  Jack is 16,  Marie is 11,  and  Fred is 22.

The lesson to learn from this solution is this trick for solving this special system of equations.
Actually,  it is the method which works in many other similar cases.  See the lessons
      - The tricks to solve some word problems with three and more unknowns using mental math
      - Joint-work problems for 3 participants  (Problem 2)
in this site.