Solving Multi-Step Word Problems with the 4 Operations: Lesson for Kids

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  • 0:04 Data & Variables
  • 0:42 Collecting Evidence
  • 2:42 Problems Involving…
  • 3:34 Problems With Time
  • 4:05 Lesson Summary
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Lesson Transcript
Instructor: Nick Rogers
Word problems are like puzzles. You need to identify the things that you know and determine how to find the answer using those facts. The things that we do know are called data, and the things that we don't are called variables.

Data & Variables

You can think of word problems as mysteries that need to be solved. First, you must collect all of the 'clues,' or the evidence. Write down everything that you know, and then decide which parts are relevant to the case. As mathematicians, we call this evidence data, while the part that we don't know is called a variable because it's allowed to vary.

Just like Sherlock Holmes, you will deduce the answer from the things that you do know. A good detective is clear about what assumptions they have to make, and a good mathematician does the same thing. Be clear about what you want to find and how you can use the resources that you have to find it.

Collecting Evidence

Let's start with an example problem. Sarah is reading her math textbook. The first three chapters had 20 pages. The last four have 30 pages each. In total, the book contains 400 pages. How many pages are in the middle chapters?

You should start this problem by writing down what you know. The first three chapters have 20 pages each. Therefore, they contain 20 + 20 + 20 = 60 pages. The last four chapters have 30 pages each. They have 30 + 30 + 30 + 30 = 120 pages. The middle chapters contain the rest. This is the data, or the things that we know.

Next, you should identify what we want to know. The question asks us very directly: how many pages are in the middle chapters? Let's give a name to the number that we're looking for. We'll call it x, so the pages in the middle = x. We can write this all down as an equation:

Pages in First Chapters + Pages in Middle + Pages in Final Chapters = 400

Now, let's replace these words with the numbers we know:

60 + x + 120 = 400.

At this point, we're ready to find x. Apply some mathematical techniques in order to do that. Subtract 60 and 120 from each side, then cancel some things out:

60 + x + 120 - 60 -120 = 400 - 60 - 120

Therefore, x = 220

After finishing your solution, you should make sure that this answer makes sense. If the middle chapters have 220 pages, and the beginning chapters have 60, and the final chapters have 120, then do we have the right amount of pages? Yes, since 60 + 120 + 220 = 400.

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