Monday, February 13, 2012

Isfeld's Math problem. Explained by me, Aniane Canuto.

Okay, I've been seeing people re-posting Isfeld's expression word problem with the answer, but there's no explanation why. 

This post will explain the following:

1. What the problem is
2. How to get to the answer
3. The answer
4. Why that answer?

Ok, Explanation number 1:

A group of students are talking, 2 students leave the group. Write an expression for the number of the students in the group after the 2 leave.

Explanation number 2:

We learned about variables, so a variable must be involved here.

We know that 2 students leave the room. And that would be a synonym to subtraction, so that 
should be involved here as well.

We have absolutely no idea how many people are in the group, so we need something to mark in the expression that proves the group is an important part of this.

Hmm...what was that word again?
Variable: A letter that represents an unknown number.

Explanation number 3:


Explanation number 4:

(Note: This is basically a retell of number 2, so you can leave at this point)

Why G?
It's a variable. We don't know how many people are in the group, so we use the letter G to represent the group altogether.

What's with the minus sign?
Students leaving the group is like a number taking away another number. And a number taking away a number is subtraction, and subtraction has the word "minus" involved.

Why is 2 there?
Because that is the number of students that we are sure of that left.

And there we have it, Isfeld's question explained entirely by me.

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