Question 404890: Mary is six years older than Jean. The sum of their ages is 20. How old is Mary
Answer by keksjr(7)   (Show Source):
You can put this solution on YOUR website! Let Mary's age be: x , and Let Jean's age be y:
Since Mary is 6yrs older than Jean, therefore it implies that:
Mary's age = Jean's age + 6; x=y+6
And the sum of their ages being 20, that also implies that:
Mary's age + Jean's age = 20; x+y=20
Therefore lets find "y" that is Jean's age by substituting x=y+6 into x+y=20;
y+6+y=20
2y =20-6
2y =14
By Dividing through by 2; y =7
Then in finding how old Mary is: x=y+6
x=7+6
x=13
Therefore, Mary is 13yrs old
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