Weekly Brain Teaser-Do you remember Algebra?

brainteaserEvery week we feature a Brain Teaser or a thought-provoking question.

If you have one that you would like to share with fellow engineers, please email it to info@engineeringdaily.net.

So, here is this week’s,

Mr. and Mrs. Ford have three daughters.

When the youngest was born, you could multiply the middle child’s age by
three to get the oldest sister’s age.

Nine years ago, you could add the middle child’s age to the youngest
child’s age to get the oldest child’s age.

What is the youngest that the oldest child can be now?

The correct answer will be posted a week following this posting.


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      1. Congratulations Daniel for being the first one to respond back with the correct answer.
        The solution,

        Ages at youngest child’s birth (youngest to oldest):
        0, y, z

        Ages 9 years ago (or x years after the youngest child was born; youngest to oldest):
        0+x, y+x, z+x

        There are two restrictions:
        (1) At the youngest child’s birth we know that 3y=z
        (2) Nine years ago, the oldest child must be the sum of her two youngest sibling’s ages, so x+x+y=x+z

        Simplifying the two equations, we get:

        From there, we input the lowest possible value of y, and calculate the oldest child’s present age:
        3+2+9 = 14

        Now, see if you can solve the next one.

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