Michael Stuart Kelly 1,319 Posted March 25, 2008 Share Posted March 25, 2008 Math problemA friend of mine just sent me a rather funny brain teaser kind of math problem. The email alleges that this problem was included last year on one of the college tests of ITA in Brazil (Instituto Tecnológico de Aeronáutica). Here is the braintwister:A mother is 21 years older than her son. In 6 years from now the mother will be 5 times older than the son. Question: Where is the father right now?Answer (which is arrived at through pure mathematics):The mother's age = Y years.The son's age = X years.Since the mother is 21 years older than the son, we have:Y = X + 21For X and Y, 6 years from now = (Y + 6) and (X + 6)So if 6 years from now the mother will be 5 times older than the son, we have:Y + 6 = 5(X + 6)Working the equation a bit, we get:Y + 6 = 5X + 30Thus:Y = 5X + 24If we replace the above value for Y in the first equation (Y = X + 21), we get:5X + 24 = X + 21Working the equation further for a pure number value on one side, we get:5X - 1X = 21 - 24Thus: 4X = -3This means:X = -3/4The son today is -3/4 year old. In other words, he is -9 meses old.The original question was: Where is the father right now?Answer: While you have been busting your brains trying to figure all this out, he is in bed right now with the mother having a grand old time! Michael Link to post Share on other sites

merjet 80 Posted March 25, 2008 Share Posted March 25, 2008 This is quicker.E1: Y = X + 21E2: Y + 6 = 5 (X + 6)E2 - E1: 6 = 4X + 9Transpose: 4X = -3Divide: X = -3/4Where is the father? Unknown. Link to post Share on other sites

## Recommended Posts

## Create an account or sign in to comment

You need to be a member in order to leave a comment

## Create an account

Sign up for a new account in our community. It's easy!

Register a new account## Sign in

Already have an account? Sign in here.

Sign In Now