Question 474181
Two sisters, Mary and Jane have a total age of 98. When Mary was Jane's age, Jane was half as old as Mary is now. What are their ages?" 
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Let M = Mary's age now
Let J = Jane's age now
Let x be the number of years ago it was when Mary was Jane's age
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Mary and Jane have a total age of 98.
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That says 

M + J = 98
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When Mary was Jane's age
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That says "x years ago Mary was Jane's age now"

M - x = J
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Jane was half as old as Mary is now
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That says "x years ago Jane was {{{1/2}}}M

J - x = {{{1/2}}}M

So we have this system of three equations in three unknowns:

{{{system(M + J = 98, M - x = J, J - x= expr(1/2)M)}}}

If you don't know how to solve that system, post again asking how.

Answer: J = 42, M = 56, x = 14.

Checking:  
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Mary and Jane have a total age of 98. 
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That checks because 56 + 42 = 98
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When Mary was Jane's age, 
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x = 14 years ago Mary was 56 - 14 or 42, Jane's age now.  That checks.
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Jane was half as old as Mary is now. 
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x = 14 years ago, Jane was 42 - 14 or 28, and indeed 28 is half as old as
56, Mary's present age.

So that is correct.

Edwin</pre>