Tuesday, May 17, 2011

How to solve a word problem...

T-bone is working through Algebra 1/2 this year and there's one problem that comes up again and again that we have working formula for.  I want to share this with you, in case it could help you with your math studies or instruction.  Here's the problem:

What number is 70% of 35?

We have had quite a few of these problems this year and t-bone is a total master of them.  Here are the tricks:

  • of means multiply

  • is means equals

  • the phrase that starts with "what" is your variable.


So, in this case, the problem would be written like this:

WN=.7 x 35

This is an easy one because the variable is already on the end.  We don't have to worry with getting it by itself.  So all you do is multiply .7 times 35 and you get the answer 24.5.  Want to try another one?

25 is what percent of 100?

Using the same method above, you just read the problem from left to right.  Start with "25 is".  The word is means equals:

25=

Then we have "what percent".  That's our variable, the word "what" is our clue.  So now our equation is:

25=WP

Then we have the word "of".  do you remember what OF means?  Of means multiply.

25=WP x

Finally, we list our last number and we have a complete equation:

25=WP x 100

Solving

Ok now we have to SOLVE this problem.  It's a little more complicated because the WP variable isn't by itself.  Anytime you see a variable or a letter your goal is to get it by itself.  Since our WP is not by itself, we need to get rid of that 100.  How do you do that?  You do the opposite of whatever it is doing to our WP.  In this case, we are multiplying WP by 100.  So the opposite of multiplying is dividing. 

Another ruled:  whatever you do on one side of the equals sign, you must also do on the other

So, we divide both sides of the equal sign by 100.  That gets rid of the number with the variable, WP.  And now we have a math problem to solve.  25 divided by 100 is .25.

WP = .25

Let's take it one small step further and then I'll be finished...I promise!

The problem asks us "what percentage."  .25 is not a percentage.  But here's the dealio, any number with two decimals can be converted to a percentage by just dropping the . and adding a %.  In our case:

WP = 25%

And there you go.  Step-by-step how to solve a very basic algebra problem.  See YOU CAN DO THIS!

1 comment:

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