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Help With Multiplication and Percents


Date: 11/11/96 at 19:24:42
From: Amanda Oakley
Subject: Math

Dear Dr. Math,

I am in grade five and have lots of trouble!  My class is a mix of 
fifth and sixth graders so we are doing percentages, which are really 
hard for me because I am not very good at multiplication and anything 
else in that area. Can you please help me?

Sincerely, 
   Amanda Oakley


Date: 11/23/96 at 15:44:27
From: Doctor Lim
Subject: Re: Math

Dear Amanda,

Don't worry so much. If you put time and effort towards your study
of mathematics, soon you will see results.  You are already taking a 
good first step by figuring out what areas are hard for you, like 
multiplication.  If this is the root of your troubles, I can try to 
help you fix it.

There is no easy way to learn multiplication.  If you understand the 
concept of multiplication, the only way to improve your skills is to 
practice what you have learned.

Most of the time problems seem difficult only because they look big 
and scary.  Problems became less frightening when you break them up 
and see them as little pieces.  You do not eat a whole cake up in one 
mouthful, do you?  You have to bite it into pieces or cut it up into 
slices before eating it, right?

So if you learn your multiplication tables, everything else will fall 
into place.  My students find learning nine times tables to be the 
hardest.  After using this method it becomes easier for them:

Put your hands flat, palms down, on the table. Number your fingers 
like this:

Left Hand       Right Hand
1 2 3 4 5       6 7 8 9 0

If you have difficulty remembering this, try writing the numbers on 
the backs of your hands.

Think of a number to multiply by 9.

Let's try 7 x 9:

Tuck your 7th finger underneath your palm.

You should have 6 fingers open to the left of your hidden finger and 3 
fingers open to the right of it.

7 x 9 = 63

Now try it out with 4 x 9:

Tuck your 4th finger underneath your palm.

You should have 3 fingers open to the left of your hidden finger and 6 
fingers open to the right of it.

4 x 9 = 36

Got it ?

For the rest of the multiplication tables, try looking at this site, 
which teaches multiplication tables as a song:

  http://www.schoolhouserock.com/multrock/   


The key to finding percents is to recognize that a percent is just a 
different way of writing a decimal.

Let us start with an example. Suppose we are given a group of 100 
people, 70 of whom are men and 30 of whom are women.

This means that 70 out of 100 or 70/100 of the group are men.
There are lots of different ways to write 70 out of 100:

  70/100
  0.70
  70 per cent 
  70%
  70% of the people are men

Let us look at another example. Suppose that in my library there are
100 books, 40 of which are big and 60 of which are small.  There are 
lots of different ways to write 40 out of 100:

  40/100 
  0.40
  40 per cent
  40%
  40% of my library books are big books. 

The notion of percent is very closely related to fractions, which you 
can see by noticing that 40 out of 100 means:
 
  40/100 = 4/10 = 2/5 = 0.40 = 40%

Math is just like a big family. All of its parts are related to each 
other.  If you can understand one part, the other parts are not that 
difficult.

Please get back to me if you have problems.

-Doctor Lim,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math   
    
Associated Topics:
Elementary Fractions
Elementary Multiplication

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