Decimals videos: tenths, hundredths & thousandths

I have now been able to get back to shooting videos after a long break. These three videos (titled Tenths, Hundredths, and Thousandths) deal with what decimals are (they're fractions!) and in that sense are tied together.

The first video explains about decimal numbers with one decimal digit (tenths) using fractions and a number line. I also include some easy addition problems.

In the second video below, I explain decimals with two decimal digits—or hundredths—using fractions and a number line. Also included an explanation of why you can "tag" or "add" zeros to the end of a decimal and its value does not change.

Lastly, I explain decimals with three decimal digits—or thousandths—using fractions and a number line. Then I show examples of converting fractions to decimals and vice versa.

Mastermind game giveaway

First of all... Math Teachers at Play 34 is online... go check out the posts!

Then... I'm doing a giveaway again... one of you, my readers, can be a lucky one to win a free Mastermind board game!

Update: The winner is now chosen, the third commenter below, named Äiti. This went quick!!!!!! Comments are therefore closed.

The lady who contacted me about it said that many of today's adults actually KNOW the game from their childhood, but don't know it's still available.

I haven't played it as a child, but a few years ago I found Mastermind online (on several math games websites), and I found I like it!

This is how Mastermind works:
You need to guess the "secret code" of colored pegs: both the color and the order they are in. You make a guess, and your opponent (or computer) tells you some clues. A black clue means you got one peg the right color AND in the right position, whereas a white clue means you got a peg with right color in the wrong position.

It's basically a logic game... you need to think logically about your guesses and the given clues.

Go play it online here (against the computer) at National Library of Virtual Manipulatives. This version is nice, as it allows you to limit the number of colors, which is helpful for new players or small children.

How to take part?
Simply leave a comment to this blogpost. Follow my blog and once you see I've chosen the winner, the winner needs to contact me with their contact and shipping info. This giveaway runs until I have 10 comments OR January 31, whichever happens first.

Which operation should you use in word problems?

I was asked just recently about word problems and WHAT operation to use in them.

Can you put a better explanation of when to use addition, subtraction, multiplication, and division, because my son is having a hard time understanding.

Many children have the same problem, and I have written about it in the past as well. In a nutshell, I feel the MAIN reason students have trouble is the way word problems are presented (or not presented) in math books.

Typically (and I still see this approach), when a lesson in a math book is on some operation, then the word problems in that lesson are typically solved using that particular operation. So, any intelligent kid who notices this pattern won't take time to decipher what the problem says, but will just take the two numbers that appear in the problem, and apply the operation that the lesson is about!

(For example, if the lesson is on subtraction, then the word problems are solved using subtraction.)

I have tried to AVOID this in my books from the start, and I think all other math curricula should follow suit, that whenever there are word problems to solve, that the operation or operations used to solve it SHOULD vary within the problem set.

Even in first grade addition, you can make two kinds of problems:

"Ann had seven marbles, and Mary had two. How many marbles do they have together?" SOLUTION: 7 + 2 = 9

OR

"Ann has seven marbles, but today she only found two. How many are missing?" SOLUTION: Think 2 + ___ = 7, or two and how many more makes seven?


So, starting in 1st grade, the word problems should never be such that they always involve the same operation. Then in 2nd grade, the word problems should proceed to easy 2-step problems.

When multiplication is introduced in 3rd grade, the word problems should be in two different ways so the child cannot automatically multiply the numbers in the problem, but has to think. For example:

Mary saw 12 duck legs. How many ducks were there?

OR

Grandma has 12 ducks, and each wore two blue ribbons. How many ribbons could you see when looking at all the ducks?

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Now, recently I had an idea for help for all these elementary students that have trouble figuring out which operation to use. I THINK it might work fairly well, but I'd like to have your input on it.

Suppose we have a student in 3rd or 4th grade who can't do word problems. What if we used the word problems in Ray's Arithmetic with him/her, starting from the beginning?

Ray's is known to be full of word problems, starting from the simplest. It sort of uses word problems to teach arithmetic. It is an old book, and therefore it is available FREE online. See the links on the left for viewing it online or downloading.

See for example the word problems on page 26.

You can also purchase Ray's as printed books.

What do you think? Could Ray's get such students up to speed with word problems?