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If Mark gives John 6 apples, Mark will have 2/3 of the apples that John will have.
Now if JOHN gives 9 apples to Mark then John will have 2/3 of the apples
that Mark will HAVE. How many apples each HAS ?
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These "virtual exchange" problems all have a standard setup.
M - 6 = (1) (If mark gives john 6 apples, mark will have 2/3 of the apples that john will have)
= J - 9. (2) (if John gives 9 apples to Mark then John will have 2/3 of the apples that Mark will have)
Simplify these equations
3M - 18 = 2*(J+6) (1')
2*(M + 9) = 3*(J-9) (2')
Simplify more
3M - 2J = 30 (1'')
2M - 3J = -45 (2'')
Prepare for elimination
6M - 4J = 60 (1''')
6M - 9J = -135 (2''')
Subtract (2''') from (1''')
5J = 60 - (-135) = 195
J = 195/5 = 39.
Finally, from (1'') find M = 36.
ANSWER. M = 36; J = 39.
Solved.
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On "virtual exchange" problems, see the lesson
- Virtual exchange between two persons
in this site.
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