Which is tallest? An elementary math problem


Which is tallest?

It’s a tricky question.  Which person from feet to head has the greatest height? Obviously that would be the first person on the left.  We will call her Giraffe.  If all 3 people were standing on flat ground, Giraffe would be the highest.

Seems like kind of a goofy question.  What is the point to this problem?

Well, actually, this is a fantastic problem.  It is full of real-world application.  Ever measure the weight of flour?  Do you weigh 8 ounces of flour with or without the bowl you are putting it in?  Or how about your own weight.  Do you weigh yourself with or without your shoes?

To be able to mentally subtract a portion in order to get the actual amount is crucial for doing science.  In the lab, scientists weigh compounds and ingredients using the tare feature of a scale.  First we put the dish on the scale and hit the tare button.  Taring the scale resets the weight back to zero.  Now we can add our chemical to the correct amount.tallestblogpicture-1

Of course you don’t need to use the tare feature.  You can place the dish on the scale.  Find that it weighs 3 ounces.  Record that number.  Now add your ingredient to the desired amount.  You want 8 ounces?  Well you will have to add the ingredient until you get to 11 ounces on the scale.  If you have 11 ounces of ingredient and the dish, you have 8 ounces of the ingredient and 3 ounces of the dish.tallestblogpicture-2

Same with this problem.  The person on the right is not the tallest, because if we subtract the base that he is standing on, he will be considerably shorter than Giraffe.  We have effectively, mentally, tared the person!

Try this exercise with your child. Ask her how much her shoes weigh.  Place them on the scale.  Do they register?  Probably not because they don’t weigh enough for the scale to recognize.  But you can find the weight of the shoes by weighing her with and without the shoes.  Can she figure out how much the shoes weigh now?

Hint: Subtract the smaller number from the larger number.

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