SOLUTION: The sum of john and lizas age is 21. If john is 3 years younger than liza, how old are john & liza? Express your answer as a ordered pair (x,y) where john is x and liza is y

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Question 1156730: The sum of john and lizas age is 21. If john is 3 years younger than liza, how old are john & liza?
Express your answer as a ordered pair (x,y) where john is x and liza is y
Found 2 solutions by ikleyn, MathLover1:
Answer by ikleyn(52776)   (Show Source): You can put this solution on YOUR website!
.

Replace Lisa (MENTALLY) by other person Mona, who is 3 years younger than Liza.


Then John and Mona are of the same age, and the sum of their ages is 21-3 = 18.


Therefore, John is 18/2= 9 years old and Mona is 9 years old, too.


From this point, you immediately conclude that Lisa is 9+3 = 12 years old.


ANSWER.  The ordered pair (x,y) is (9,12).

Solved.

At this point, you may forget about this person Mona, since it was "imaginary" person, introduced to facilitate the solution, ONLY.


Answer by MathLover1(20849)   (Show Source): You can put this solution on YOUR website!

john is and liza is
if the sum of john and liza's age is , we have

.....eq.1
if john is years than liza, we have
.........eq.2, substitute from eq.1
........solve for



go to
.....eq.1, substitute

answer: (,) where john is and liza is


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