Question 1011390
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10 years ago, Mona's mother was 4 times older than her daughter. 
After 10 years, the mother will be twice older than the daughter. Mona's present age is:
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Let x be the Mona's present age, and let y be the Mona's mother present age.

Ten years ago, Mona's age was x-10, and her mother's age was y-10.

Since ten years ago Mona's mother was 4 times older than her daughter, you have an equation

y-10 = 4*(x-10).

After 10 years, the mother's age will be y+10, and Mona's age will be x+10.

Since after 10 years, the mother will be twice older than the daughter, it gives you the second equation

y + 10 = 2*(x+10)

Solve this system for x and y:

{{{system(y-10 = 4*(x-10),
y+10 = 2*(x+10))}}}.

<U>Answer</U>. x = 20. Mona's present age is 20 years.
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