Question 978540
How would you solve this? Mary is presently 12 years older than her sister. Four years ago she was twice as old. How old are they now? 
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Equations:
m = s + 12
m-4 = 2(s-4)
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Substitute for "m" and solve for "s":
s+12-4 = 2s-8
s = 16 yrs (sister's age now)
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Solve for "m"::
m = s + 12
m = 16+12 = 28 yrs (Mary's age now)
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Cheers,
Stan H.
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